So, OP, I will say that I'm a little on the younger side--I just started my first year, and I'm 21. I've had no issues getting along with my classmates, even those who are significantly older (in fact, the classmate I'm closest to is 28). I do have some trouble in the social setting, but that's more because of personal choices (don't drink, don't like going out, very introverted) than an age difference. I've also had no issues with maturity or taking responsibility.
I have gotten a lot of the advice that you're getting in this post about taking a gap year or living a little from many people I've met. Because this feedback is from people who are older and wiser, I do take it seriously, but frankly, I'm uninterested in that stuff. This might sound silly, but as a woman who has both a lot of career aspirations and a desire to have a family, I like knowing that I have more time and maybe even more flexibility than my peers; I've talked to some of my older female classmates (I guess men might worry about this, too, but in my experience, women do more) who don't have kids yet who are worried about when to do it, because they don't want to wait too long, but they also don't want kids in residency, etc. Some of them are avoiding fields like surgery where postgraduate training is longer, whereas I feel like all the doors are still open for me. I'm thinking about getting an MPH maybe, and because I'm so young, I don't have to think about that extra year as much as older peers do. Some of my peers have said that they wished they'd realized they wanted to go to medical school earlier so they could've started earlier. Others, though, have had great experiences doing research or teaching with Teach for America, so I think it's all really on a case by case basis.
It all depends on whether or not you're ready, though. If you think a gap year would be beneficial, do it, but don't do it because of fomo (my general rule being that doing anything for the sake of fomo is a bad idea), do it because you really want to. And if you are sure going to med school is really what you want to do, I encourage you to go for it.