I'm only 18,....been 18 for over 20 years, and plan on being 18 for at least another 20.
I think when you're younger there is alot of artificial importance put on age difference. As we get older that emphasis is quickly dropped in favor of mental maturity.
For example, I would much rather discuss the intellectual nuances of Family Guy and South Park episodes with a mature 16 year old than an inmature 36 year old.
The fact that most of my friends are younger than me, and mature, responsible, intelligent, and fun people, hints to me that I am still young at heart. Exactly where I want to be.
Customizing bikes takes creativity, originality, appreciation, and is essentially just a fun and practical(for the most part) hobby,....there are no age requirements or exclusions needed.