As millennials get older, their financial ambitions mature too. TD Ameritrade's recent "Millennials and Work" survey found that the average amount millennials (defined, in this case, as those aged 21 to 37) say they need to earn be happy has risen $30,000 since 2016, jumping from $50,000 a year to $80,000. Nearly a quarter of millennials (22 percent) say earning between $50,000 and $74,999 a year is what it will take to make them happy, while 41 percent say they'll need $75,000 or more. That's significantly more than young people actually take home: Those between the ages of 25 and 34 earn a median salary of just $41,288 per year, according to the BLS, and SmartAsset estimates that those 19 to 37 years old earn an average of $35,592. Still, there's a strong contingent of millennials — 22 percent — who say they can earn $25,000 or less per year and keep their spirits up.

Click to enlarge. Older millennials tend to say they need a larger amount to be content: Those 30 and up report needing an average salary of $101,500, while respondents under 30 average only about half that, or $53,500. As millennials age, they're earning more and starting families, and their aspirations are keeping pace, Chris Bohlsen, a director in investor services at TD Ameritrade, tells CNBC Make It. And as they get a better idea of what they have the potential to earn, they're able to set higher expectations about what it will take to make themselves, and their families, happy. Having kids matters as well: Nearly 40 percent of respondents with children say that they need over $100,000. "There is a need to provide a higher quality of life for your children," Bohlsen says. "When you have to take care of somebody else, you give yourself something bigger to shoot for."