Like anyone, those in Gen X and Gen Y can’t always avoid making mistakes with their money. But there’s plenty they can do to correct mistakes, especially because most of them have enough time — Gen Xers are those born between the ‘60s and the early ‘80s, and Gen Y folks and millennials, born between the early ‘80s and the early 2000s.

So we asked some financial-planning experts what mistakes people in these age groups are making, particularly in regard to their retirement planning, and what they can do about it.

1. They don’t get professional help

Andrew Sivertsen, a certified financial planner with The Planning Center in Moline, Ill., said biggest retirement mistake is not the fault of Gen X and Gen Y, but the fault of the financial planning/investment advice profession. “These demographics are greatly underserved, yet most major financial decisions happen before we’re 40,” he said.

So what’s the problem with the profession? According to Sivertsen, the profession has built its compensation structures around commissions or assets-under-management (AUM) models that make it difficult to serve this demographic because of their lack of assets.

Consider: many well-established advisers require that clients have $1 million in assets for which they would charge 1% to manage that money. But what do Gen X and Gen Y have in assets? Not that much. Americans under age 35 had on average a net worth of just $10,400, according to the Federal Reserve’s Survey of Consumer Finances. So, no money, no advice.

One solution: Advisory firms could adopt retainer models or monthly subscription models that can make it more affordable for this demographic to find advice, said Sivertsen.

Gen X/Yers might also consider using robo advisers which tend to have lower initial investment minimums and lower fees. The trade-off is that you might not get the same sort of financial-planning advice that you might get from a human, but at least you’re getting investment advice. The other option would be to find a financial planner who charges by the hour. You can find such adviser in the database at the Garrett Financial Planning Network.

2. They lack savings

Sivertsen said the biggest looming threat to Gen Xers, however, is not access to affordable investment advice. Rather, it’s their lack of savings for retirement. And it’s a threat made even worse if you consider the possibility that Social Security might not be available in its current state for their retirement. Social Security benefits are expected to be payable in full on a timely basis until 2037, when the trust fund reserves are projected to become exhausted. And, at the point where the reserves are used up, continuing taxes are expected to be enough to pay just 76% of scheduled benefits.

What to do? “Some of the possible solutions include increasing savings and possibly decreasing education savings for kids,” said Sivertsen. “They may need to have other conversations with their children about how to deal with the cost of education.”

Others agree. “The single most common mistake those groups make is failing to save at all,” said Jamie Cox, a managing partner with Harris Financial Group Richmond, Va.

But one of the more interesting mistakes, he said, is the tendency for these groups to prioritize saving for their kid’s college rather than their own retirement. “They fear insufficient means to fulfill a college dream for a child more than having a major lifestyle reduction in retirement,” Cox said. “There is no single financial gift a parent can give to a child that matters more than being financially sound in retirement.”

Gen Y, meanwhile, has a different threat. Sivertsen believes that most are already not planning for Social Security and saving more to compensate. Their bigger threat, he said, is not investing in themselves and their human capital. “Partly due to the recession, and partly due to wanderlust to see the world, many have been unemployed or underemployed,” he said. “By delaying settling down into higher income careers, many will have to save more later on to catch up.” Read Invest in yourself to maximize your return on (human) capital.

3. They don’t take full advantage of employer match

Gen Xers and millennials often fail to contribute enough to their 401(k) plan to receive their employer’s match. Many employers contribute 50 cents on the dollar up to 6% of plan participant’s contribution. But studies suggest that about one-third of workers don’t contribute enough to get the full match.

“The biggest mistake is leaving money on the table,” said Rianka Dorsainvil, a certified financial planner with Financial Services Advisory Rockville, Md. “Most Gen X/Yers do not know that their employer offer matching incentives for their retirement plans. Some companies may offer 6% matching, but if you are only deferring 4% of your salary, then you are leaving 2% of free money on the table.”

Read One-third of plan participants are giving away free money ... are you?

4. They are saving only in their 401(k)

Younger people mistakenly save only in their retirement accounts. Yes, saving for retirement is important. But it’s also important to save using many different types of accounts, said Laurie Belew, a certified financial planner with FJY Financial in Midland, Texas.

“It seems that many neglect saving to an after-tax brokerage account,” she said. “We all know that we should diversify our investments, but what about the diversification of account types?”

Setting aside assets that can be accessed without penalty before 59½, said Belew, is an important piece of the plan, as well.

“We should focus on balancing where savings dollars go so that we can master the trade-off between retirement and other financial goals,” said Belew. “Not to mention, arriving at retirement with only tax-deferred savings provides little flexibility for managing taxes during retirement.”

5. They don’t invest in stocks

Mark Berger, a certified financial planner with Berger Financial Group in Plymouth, Minn. said Gen Xers and millennials often don’t let their investments to work hard enough for them.

Younger people seem to avoid “stock market risk, because they do not understand the impact this has through time,” Berger said. “Having lived through the two severe downturns in the past 15 years has created this cultural opinion.”

What can be done to correct this mistake? Berger gave this example: Saving $100 a month that grows at 9% over 30 years is almost the same as saving $300 a month at 3%. In other words, it’s equal to saving three times as much — if you let your money work properly.

So consider these solutions and avoid these mistakes, the sooner the better.

You’re invited ...

What do federal proposals to impose a fiduciary standard on retirement advisers mean for investors and advisers?

MarketWatch is holding a special Retirement Adviser event at the end of July to explore these issues.

If you’re planning to be in New York on Tuesday, July 28, you’re invited to an evening of cocktails and conversation on the Fiduciary Quagmire. The event is free but reservations are required.

In this panel discussion, experts will explore investors and advisers need to know about the current state of the proposed fiduciary standard for retirement advisers, and what changes they might make to their personal financial plans and practices/businesses in the wake of whatever final regulations are put in place.

Our moderator for the event is Mark Hulbert, MarketWatch senior columnist and editor of the Hulbert Financial Digest. Our panelists are Robert Powell, senior columnist and editor of Retirement Weekly from MarketWatch; Knut Rostad, president and founder of the Institute for the Fiduciary Standard; Ira Hammerman, executive vice president and general counsel for the Securities Industry and Financial Markets Association; and Brad Campbell, attorney and former Assistant Secretary of Labor for Employee Benefits and head of the Employee Benefits Security Administration.

The evening begins with cocktails at 6:30 p.m., followed by our panel discussion and a question-and-answer period. Seating is limited. If you are interested in attending, email MarketWatchEvent@wsj.com for more information or to RSVP.