I Will keep him until he continue to perform. Dont look to mutch for the quality, look for what that player makes in the field.
Last season i had a 34 years old ML/AML 1* and he still scores 9 goals(100 goals total for the club) and made 9 assistes, 2MOM.
It is better to have a player with low quality in top form, that one with high quality with bad form.