Players have a hidden aggressiveness attribute already. They foul more and are less afraid of contact when driving. You can argue that IS and DR training is more effective for this type of players so essentially "faster".
As for a youth team, you could always have 5+ youngsters and play them during scrimmages, but you can't train different skills for your starters and for your youth the same week, I guess.
"Air is beautiful, yet you cannot see it. It's soft, yet you cannot touch it. Air is a little like my brain." - Jean-Claude Van Damme