OK a bit of backgroud info first...
I had been shy throughout my school life but since leaving school 3 years ago I have become more confident than I ever thought I would be. I did have a few good friends at school who I still meet up with when there back from university but this isn't very often. But when there away at uni I feel I don’t have any friends. Basically what I'm saying is I haven't got many friends and am stuck for ways to find new friends.
I have good career prospects and enjoy where I work so I don’t really want to move away but at the same time I work with people who aren’t in my age group. The youngest people I work with are about 29/30 and starting to settle down with girlfriends and marriage.
I feel stuck in a rut as I'm not going out and am stuck indoors. I like tennis and used to play at school but I don’t know how to get back into it and I don’t know anyone who plays. I'm only 5ft3 and not very strong so football clubs and rugby clubs aren’t for me. I'm basically stuck, got hardly any friends and don’t know where to go next. If any one can help it would be greatly appreciated. Thank you.

PS sorry it's a bit long

You like tennis? Great, join a club and have fun. Pick activities you like, find clubs or organizations that offer this sort of thing and join in. Being an introvert I find it extremely hard to make small talk, so to counter that I am a greeter at my Church. Get the idea. Life is what you make of it, not what others make you think it is. Your best or lasting friendships will be made through places where you enjoy being, or activities you enjoy doing.