It should be drastic.
All important skills points plus stamina added up "total" drop by %
Rough numbers e.g.
30y 2% per season
31y 4%
33y 6%
34y 8%
35y - 40y 10%
My 35y player in example with 382 total points on his 7 important skills should lose 38 points this season.
382 x 0.10