This would be another significant improvement for KOB, in my opinion. Currently, players reach their peak on the day they retire, which is unrealistic. Why should they retire at 35 if they are better than ever and projected to keep improving until 38?
But how could this be implemented? I suggest taking inspiration from the best games, such as the SI Football Manager series, where players' skills gradually and slowly start to decline at 30. However, this decline is counterbalanced by training, with the rate of decline increasing with age and influenced by their natural fitness. As a result, players who train well and possess high natural fitness can continue to improve for several seasons after 30, while others peak around 31–32. Physical attributes decline faster than technical skills, while mental attributes remain largely unaffected.
I would avoid implementing this as a random decrease, as that could frustrate users. Instead, it might be better to have a small daily decline or even a reduction calculated at the end of the season, with the amount depending solely on Age and Natural Fitness. In addition to enhancing realism, this adjustment could improve the transfer market, as older players who are no longer suitable for top clubs could still contribute significantly to lower-tier teams, particularly because of their leadership. And top clubs will probably have to buy youths more often, which means more money to the funds and higher prizes for the competitions