What time of year do you start pitching training for 12U?

My son will be playing 12u next year and I would like to get him working with a pitching coach before next season. He isn’t playing in the fall and hasn’t pitched since late June. I am trying to follow the Pitch Smart guidelines and give him at least 4 months off a year.

Just curious when the best time to start throwing would be?

Give him 4 months of rest or just wait until January or do something different?