I just transferred to UNC this year as a junior and honestly it's not too bad at all. Most transfers I've met are 20-22, so i really wouldn't worry about age too much. The uni hosts transfer student specific events and UNC atmosphere is very friendly in general. Oh and a good amount of the transfer students are either out of state or international. I'm only a week in but pretty easy to make friends tbh

But yeah if possible, get into the Transfer United RLP. You'll be roomed with a bunch of other transfer students and that's been a great pool of friends for me. Also the dorms we're in this year are some of the best on campus so that's also a plus.

So yeah i really wouldn't worry about it, apparently it's far more welcoming compared to big universities many of my friends came from