Actually, I think the requirements are (a) either an elder, MS, or pioneer, or (b) 20+ years baptized.
You could have a 19 year old MS or pioneer.
Although, it's hard to imagine a 19 year old with $5000+ to blow on a one week trip to a convention.
Then again, there are a lot of teenaged slackers, sorry, pioneers with wealthy JW parents who subsidize a life of ease, sorry, a life of whole-souled service.