Young players usually have 4* and 2*, buuuuuuut if you receive them the first day of the season, if you were promoted they "lose" one star. Additionally, they are 19 yo instead of 18. It's clear that it is a Bug, I was struggling with Nordeus last season, but it's pointless, they don't want to admit it.

So be careful, try not to receive Young players the first say of the season...