Should I keep this 119% player next season or sell it ?

[USARABAT]

I usually sell players at age of 21 -22 but since I joined this forum and saw many awesome screenshots about managers keeping old players with hundreds of matches and goals ... something changed in my mind ... of course not every player is a legend ... so I will try to summarize my observations and request your advice about if I should keep this player and give him more chances or no ...

This guys did an awesome job the first two seasons ( age 18-19) by scoring almost 1 goal every two matches and doing many assists ...
His marks were almost 7/8/9/10 over 10...
At age of 20 , i noticed that his scoring rate / sense slowed down / decreased and this season ( age 21 ) I kept him on the benches almost all the games since he betrayed me last season

His stats are shown below ...


My questions :

Do all legends pass through low scoring seasons/periods ?
Should I give him more chances as a starters or as a substitute or sell him ? thanks Attachment 87628Attachment 87638