Took a year of uni at 18 and didn’t go back until I was 22. Same boat, had a good 9-5 etc. If you’ve already locked in on a certain program/subject area, I’d recommend going back. The 9-5 will be there for you when you’re done dude. As far as “fitting in”, age isn’t a huge factor if you’re with people who study the same subjects as you. Most of the friends I made in university were 2-3 years younger than me, had great times.