The stars depend on the quality of your youth facility. Last season I had the building at L3 and got a 3* (12 tokens AFAIRC) and a 1* (free).

I got both mid-season. Im signed the free 1*, checked his growth and was massively pissed. It would not have been possible to improve him to 3* and sell him until the end of the season, so I dumbed him. I tried to approximate the market value of the 3* and got a far better ratio than a money transfer (even one level higher). So I signed him and let him train with the team to become 4* and then sold him. So signing the better one for tokens made sense in my case (to me) at the start of the game (im Lvl 3) since money is a bottleneck. Keeping the bad one in the squad until the 1st day of the new season would have made sense when thinking of the new cup format, too. But I did not know it at that time.

You wrote you get both at the end of the season. That is BS. As Poker-32 already wrote the players get quickly one year older and decrease in value. I would suggest to dumb the better one that costs tokens and sign the other one for free, watch how pathetic he improves and dumb it after the cup draw has been made (1st day of new season)