Sometime around 25, maybe 27.

Some people catch old a lot sooner than others, though

Mid to late twenties you have enough experience and perspective to be reasonably considered adult.

Somewhere between 50 and 60, I think.

So, at what age do you think someone becomes a man?

My take is that you’re a full adult when your pre-frontal cortex is fully formed, which happens at around 25 years of age