I don't use mods, so I'd love for this to be included in the game. As others have said, I want some sims to be eternally bad at certain things and eternally good at others (and not progress). It could even be a cheat. Something like shift-clicking on your sim and selecting "disable skill progression" and choosing which skills you would like to disable progression for (or it could just disable all skill progression). Then, if you want to re-enable it, you could shift-click your sim and select "enable skill progression" and choose the skill. This is an awesome idea that I've wanted for a while. I hope it can be implemented! :)