It always depends on your situation. If you care about winning a lot and get trophies and you have no problem with playing a lot of boring games vs bots or inactive players you can choose to manipulate draw and sell your older players like you showed above. Personally I would sell all players 25 years and above who are 90% or below. Again, depends on how much token and money you got.
For training I only do it on the beginning of a new season, again it is up to personal preference. But for draw manipulators especially this is a good strategy.