@Claudia ************
Never ever heard of a age limit as a max..
Many just chose to change to a non o/a visa when they become 50 because that is the minimum age for what many would call a retirement visa after it's more easy even they still like to maybe study Thai.
If there was a max limited be sure all schools would ah e itt mention in their websites.
So no source other then haven't heard about and the logic part whee schools would mention it hope that make sense to you