I had a 32 year old player at 42% retiring, he was top league rated, top goals scored, most MoM that season.
Last season my ST was 40%, second lead scorer.
40% defender rated as well as 18-27 year olds much higher Q%.
I used 2 subs ≈20%, both rated 7-8 in their sub matches.
My team was 3rd in league, way under -20% compared to other top 8 teams, but we beat the winner 2x in league +2x in CL.

Quality doesn't not matter as much individual player talents.

Without veteran players losing 1 star, managers cannot make the skill points balance well. It's important to adjust players each season.

This season I will players 20% in my starting line up, it's not a risk for me. Some players stay consistent in rating, some drop slowly, many must be fired eventually. But managers should look for old players who stay strong.