Training for 24 hour events

I was wondering how everyone trains for 24 hour events. I dont plan on finishing first, I plan on completing it. Also, does anyone know the youngest age to have been able to complete a 24 hour event? Im shooting for that, ive already done several succesful races and my eyes are now set on completeing a 24 hour event.

Currently my training consists merely of riding trails. Should I start using post-workout gels such as accelerade? I dont plan on dumping tons of money into my bike or anything, I just want to know how to get in shape...

Thanks