Teen needs to shape up at school
One thing you didn't say was if you tried using the graduate early option on Mei when you had the teen talk to her. Did you try that?
For what you said though, I agree with you. The teen is probably glitched somehow. I can think of a couple of things that might clear it. Neither of which is guaranteed to work though. And both should be done in a test save to see if these will work first before trying it in your main save.
1 - You can try making the teen a child again using the CAS cheat. After you exit CAS, then take the household back to CAS and age him up again.
2 - You can try saving the household to your library then deleting the original and then loading the copy back into the save from your library.
3 - You can do this with the just the teen too by deleting the other household members, saving the teen to your library. Once you have the teen in the library, exit the save without saving and reload. Then take the household to CAS, delete the teen and add him back from the library. You'll need to activate the CAS cheat before you do that so you can reset the family relationships.
If you're playing on a PC or Mac and use Mods, you can accomplish deaging and setting relationships with MCCC. You'll still need to go to CAS to delete the sims and add them back. If you're playing on a console, activating the CAS cheat will probably disable achievements. So, only option 2 will get it done without disabling achievements.
Or if you don't want to do all that, you could simply age the teen up to YA with a birthday cake.
Hope this helps.
