Yeah, team trainings work best at the beginnings (pre-Cup) and ends of the season, weeks where you forget to schedule or miss the scrimmage deadline, the All Star Week. Especially if your early league schedule is tough, game shape training in the early weeks can help you be more competitive, in theory. I'd rather still train skills, so I've been doing FT almost exclusively during those periods. Plus, I've seen JS pops while training FT.
The answer to your other question is more complex...lately I've been preferring 19 yo with better starting skills, primarily because I am still learning different training strategies on my own, and feel they are generally of better quality than had I trained them for a year :) However, if you want maximum revenue from selling the players, 18 year olds are still more valuable, because each year is significant for training...so someone who is an effective trainer, that extra year is gold.