Selling players at end of season?

[Datis-apina]

Hello,

I am currently level 2, and I want to know which players to sell at the end of the season.

I know how the transfer market works, but at what time should I sell to get the most bids? I am on GMT +1

At what age should I sell players?
Should I sell anyone going to 3 star rating?
Should I sell young talents that haven't played much?

I am looking to get up to a decent 5 star level as quickly as possible next season, but many of my best players are 26-29 year old, so I'm afraid that they won't make it to 5 star, although they are 29/30 rating now.

What do you guys think, especially high levels, how do you handle the end of the season?