Solved

staff 20tal 19exp 20mor is 4.5stars

then, i understand stars has nothing to do with attributes. nothing at all. Am i right?

thanks

Goodluck getting an answer Dan

The star rating of staff is tied to your manager level.
If you're level 17, and the staff is level 16, then they're likely to be a 4 star or 4 1/2 star. If you were to level up, that might drop to 3 1/2 stars or 4 stars.

Yes, the stars result from manager level compared to the level of the staff.

The level of staff is connected to the attributes but Dan has a point there, there is something else. It might be age playing a role but I didn't find a pattern there, but that might be because attributes of different staff may be differently weighted and you don't often have 2 staff of the same role or, probably, since it didn't worry me enough I haven't compared similar staff on the transfer list, yet, so data was very limited and far apart. So it could be age or something completly different like good looks for all I know.