Age doesn't really matter at uni. One of my friends is 24 and I'm 19, and then another is 22 and all her friends are 19. It's unnoticeable.
I think you're more likely to make friends with people via your course and accommodation, who will also all be first year. You may meet third years via societies and sports, but I don't see why you'd want to form close friendships with them as they'll probably only be around uni for a year, and then who will you hang around with in second and third year?