[Bells]

Generally, I'd say 20-25 because by that stage main education is complete, and men have time to find a job and be independent if they need to. Also, if they go to university they leave even before then and by 20 should be more settled.

However, I agree with those saying it's fine for a man to continue living with his parents, but in order to learn some independence it's better if he's not dependent upon them, and has his own job, takes responsibility for everything, etc. The just living with them part is therefore acceptable in many cases.