I haven't made it to the flight deck yet (currently training) - but I'd say Go for it!
If you're worried about your eyesight, check the Class 1 medical standard here
http://www.caa.co.uk/default.aspx?ca...90&pageid=2189 (opens as .pdf file, right-click and use "Save Target As")
I know people your age who are currently training with me (I'm 22) and they don't have a problem. Likewise, the people who are doing well on my course don't need to be physics/maths geniuses, they are the ones who really want to fly and are applying themselves.
Well worth a try if you really want to - good luck!