First of all, let's get it straight, it is not about the age or something. It is about the kind of person you are going on the date with. Why is that even important to know? Well, what if you fall for them, God help you.
Anyway, that can't be helped, what can be, is knowing what you are getting into.
The most important part of a relationship, a man will give you the respect you deserve including your privacy over issues and space, while a boy will be jealous and continuously poke in your life. Also, a man will be trustworthy and focused while a boy might go cheat or collapse in difficult situations.
The aura of confidence, the sense of control over self and elements around is only seen with men and not boys who tend to be insecure with you and themselves.
A man his mind straight to what he's headed towards while a boy may be careless about his future and what's worse is he finds it cool to be aimless, there is a warning attached with such a person.
Everyone has some responsibilities to fulfil while a man will keep his word making him dependable, a boy would be found running away from them.
This is the key to discovering most of the traits. A man will be easy with communicating and will listen intently too. On the other hand, a boy will rather brag but won't be able to express his emotions neither grasp yours.
An extension to the previous point, calling up shows the commitment of a man towards you and also his loyalty, a boy will mostly prefer to text, might as well be because of him talking to others too.
That who is stable, and is man enough to talk about his future with you is the one. Boys won't do that, most won't be stable enough to support themselves leave alone you.