I think it depends on the person regardless of their age.
My kids DD(15) DS(13) DD(10) all love it and have been involved with the trading part since 1999 (they have been collecting since they were born because DH and I collect).
Our nephews have been involved for a few years also, one is 20 and the other is 17, our niece although she has pins from us just had her first trading experience in 2003, she is 5. (all 3 of them have filled their lanyards and now have pinbags)
Our other 3 nephews twins (5) and a 2 year old (who as a matter of fact just got 2 more pins off of Auntie last week when we were practicing pronouncing the characters names) have pins from us, and will have their first trading experience this May, on their first trip to Disney.
Some of the rest of the family collects but doesn't trade.
All in all, let him "feel it out" he might enjoy it. Once he sees that this is something for all ages his interest might be aroused.
Have a great time!!