I've just started cycling to/from work once/twice a week. I'm 27, and not diabetic however i'm fairly certain I saw a pregnant woman pushing a pram up a hill faster than I was cycling.
The way I look at it is i'm having fun (on the down hill bits) and am doing myself some good so it's all worth it in the end.
Keep at it, and think of all the money you're saving which can then be spent on the car
