Question, will your son be a pitcher only?
JMO but the coach should be helping your son to develop a routine, unless he has no clue what a 14 year old should be doing.
Keep it simple. You dont want to burn out before he pitches.
Run poles until he breaks into a sweat, this tells you are warmed up. With rest of team, throwing warm ups with partner. Bullpen to practice pitches. Set on a specific number amount depending on how many pitches he has. At his age he only needs 2-3 pitches. His fastball the #1 pitch. Don't forget to stretch. If he is not a pitcher and hits, he can take batting practice.
Again, keep it simple. He is 14.
Thank you, appreciate the time for a reply.
Just to be clear, the coach will be helping to develop a routine, but the coach has asked him to develop something initially on his own. They will then review, discuss, and tweak it together. It's part of the coach wanting him to take ownership of what he's doing, as they do spend a lot of time reviewing warmups, armcare, etc.
He will not be a pitcher only, but he will be one of the primary pitchers, was told he would usually be starting on a weekly basis, 1-2x a week depending on pitch counts, etc. In the past, he wouldn't know if he was pitching until asked really, so this is new to him.