Age is a factor in several Asian countries and often there is a cut off age, though sometimes exceptions are made.
Older teachers are perceived by some as being more likely to have health issues, low energy as well as being set in their ways. The public school board in Korea, for example, has lowered the age limit for public school teachers from 55 to 40, and 45 for teachers who have a lot of experience or education behind them.
Most schools prefer younger teachers in their twenties. This is perhaps because they can pay them less and manipulate them more easily. However, there are certainly many schools around the world which prefer older teachers as they feel they can bring authority to the classroom as well as greater experience and style to the lessons. Although most jobs won't specify an age limit, it is as well to let the school know when you apply how old you are to avoid them turning round and canceling everything once you send a photo over for your visa.