A Guide for fast trainers

[nikolgiorgos]

18-21 yo train the same,after 21 they train slower.

correct.
The only thing to consider is if it's worthy to invest your greens in a 21 y.o. player (as there might be a general plan to get rid "older"/slower trainers at the end of that season.

Question : 'right' time to use the greens is at the 1st day of next season?

Yes, day one it's good to start the power training as you already know your opponents in Cup and CH.L. and "study" them (quality, roster, age of players, budget, previous trophies, asso groups).
I observe also that many oppo from your Cup draw happening to be in the same League draw (which is also ready but we can't see it yet).

but I would say that it's better to wait till Monday night, when you have made some new transfers and complete a big part of the roster.