I don't think there is an age that's too old. I'm 31 and have been playing since I was 13. I went through a period of 7 years where I didn't touch the guitar, mainly due to the bitching of my ex wife everytime I thought about picking one up. I'm not the greatest and I admit it is depressing to run across someone who's significantly younger and can really shred. I have noticed a big difference between younger guitar players and older ones though.

When I first started playing, all I wanted to do was play songs. I had no interest in chord progressions, modes, I,IV and V chords etc.. I just wanted to play Ozzy, Metallica etc.. As I got older I realized that I could play a song note for note but I didn't have a f#$king clue as to why songs were structured the way they were. I also realized that although I could play them note for note, if I had to improvise I was totally lost. So I went back and starting learning the theory of playing guitar. Instead of being Jimmy Page, Randy Rhoads, EVH etc.., I started developing my own style which combined all my influences. I'm not as fast as I used to be by far, but when I play now, I put more feeling and emotion into it. Now, for all of those of you that are younger, I mean no disrespect. This is a generalization. I'm sure there are younger players out there who have already developed their own style, but most guitarists I run across these days between the ages of 15 and 25, most are just copying other players note for note.

I guess the bottom line is, it doesn't matter how fast you can run up and down the fretboard, use a three fingered technique or thrash with the best. What matters is do you invoke emotion not only from those who are listening but in yourself? That's the true soul of a guitar player and his/her instrument. Steve Vai can run circles around Eric Clapton when it comes to speed, but who do you think more people will list as an influence now and twenty years down the road?