Toms View of the World

Here’s a question, which I don’t seem to be able to find an answer to…
How old are you when you stop being “young” ?

The prompt for this question, is my pondering where I am personally on a scale of “age”… Now I’m 31, so I’m certainly not “young” any more, and there’s no way I’m “old” yet - however, I don’t think I’m “middle-aged” either - so I thought I’d ask you lot - my readers… give me your opinions!