I have a suggestion for the graduation system.
1. I would really love to be able to keep my Idols longer. All of the idols graduate usually at a young age like 18 or 20 years old. It would be amazing for them to still be an idol all the way up to age 30-35. I don't really like how I have to keep finding other idols by doing auditions just so I can replace my graduated idol.
2. Instead of having a set graduation date (they should always graduate/retire if they reach 30-35 years), it should be the idol's choice to graduate or not until they reach the max age. Idols could graduate if they decide to stop being an idol (could depend on mental stamina if it gets too low or they are involved in a lot of scandals, being bullied for too long, etc.). They could also leave because of a personal reason (maybe their family member died, if they are young and still in school; they can leave to continue studying, etc.).
3. If the above suggestions are suggested, it could also be added that idols can return (if accepted or declined by the player) back into the group if they graduated early before the max age. For example, a idol could've graduated to continue studying but decided to continue being an idol instead.
4. Would also like to add the idea of trainees. Trainees can be trained until the player decides to debut them. It would add a more realistic feel to the game. I think it would be awesome if we could list 12-16 year old idols as trainees and be able to debut them at 18 or so with their updated attributes.
Hope you take these suggestions into consideration. Most of all, I really hope you can adjust the graduation ages to be higher instead of the normal 19 or 20 age.