Forty-five percent of adults say they find it difficult to make new friends, according to new research.

A new study into the social dynamics of 2,000 Americans revealed that the average American hasn’t made a new friend in five years. In fact, it seems for many that popularity hits its peak at age 23, and for thirty-six percent, it peaks even before age 21.

The study, conducted by OnePoll in conjunction with Evite, uncovered that one of the reasons 42 percent of adults struggle to make friends is due to introversion or shyness. And the challenge isn't just in breaking out of one's shell, but also breaking into new social situations and circles.

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The majority of respondents cite friendship-making barriers that include aversion to the bar scene, where most people choose to socialize, or the feeling that everyone’s friendship groups have already formed."

Other notable reasons Americans can’t seem to make new friends, as an adult, include commitments to family (29 percent), not having any hobbies that allow them to meet new people (28 percent) and moving to a new city (21 percent).

Though adults find the struggle to be very real when it comes to making new friends, they are open to suggestions for expanding their social circle. In fact, 45 percent of those studied reveal they would go out of their way to make new friends if they knew how, or had more opportunities.

"For the 45 percent who are looking to make new friends, the best and most underrated way to do that these days is still in-person," says Piera Pizzo, Evite's in-house party specialist. "You can host a party, or something more low-key like a book club or happy hour, and tell each of your guests to bring a friend. You'll be surprised at how naturally social circles can come together, and at the lasting connections you can make when bonding face-to-face."

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And how many friends do adults actually have? Turns out, 16. The average American has three friends for life, five people they really like and would hang out with one-on-one, and eight people they like but don’t spend time with one-on-one or seek out.

Most people have remained close with friends they met when they were younger. Nearly half of those surveyed have stayed friends with peers from high school, and a further 31 percent with peers from college.

Kicking it even more old-school, three in ten Americans say they have made lasting connections with people they met in their childhood neighborhood.

However, 82 percent of those studied feel like lasting friendships are hard to find. The number one cause of lost friendships is moving away, with 63 percent revealing this to be a reason they’ve fallen out of touch with a former friend.

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With no shortage of challenges to staying in touch with friends, how can Americans ensure that growing up doesn’t mean growing apart?

"We know better than anyone else that nothing happens unless you get it on the calendar," Pizzo suggests. "Whether it's a casual bi-weekly dinner with local friends, or an annual trip for long-distance ones, take the initiative to make and set time for the people you value in your life. That time is even proven to make you happier and healthier, so there's no reason to wait."