I'm 24 and still a virgin because of the way I was raised. My friend said I'm too young and not mature enough to be with her though she knew my age before going out with me. Is it true that you're really a man once you've had sex?

There are 3 sentences in your question.

They are not connected in any obvious way.

Are you a virgin at 24 because of a moral conviction, or were your parents so scared of your being in a sexual relationship that they did not allow you sufficient interaction with females to develop sufficient comfort when being with them and interacting with them?

If the latter, her reason for saying you are not mature enough for you may well have absolutely nothing to do with never previously having had sexual intercourse.

And what makes one a man?  Read Kipling's poem here:

www.poets.org/poetsorg/poem/if%E2%80%94

You are a man when you stand up for your convictions. There are many childish males having sex without taking any responsibility for their actions.perhaps the woman you are seeing is not the right one for you and you need to move on. You need to find someone who appreciates you and your beliefs.

Having sex dont make u a man.real men show tears of joy and pain

I find that "Really Being a Man" falls under several criteria:

• Being responsible for your self and your actions both good and bad
• Have a code of honor. Even though it may not be the same as someone else's if you stand by IT and your word, then that's something.
• Make the hard choices yourself. The really difficult life changing choices, need to be dealt with and not handed off so if things turn out bad you have a scapegoat. 
• Allow yourself to take pride in those things you excel in
• Be okay with making mistakes. This will ensure that you live your life to it's fullest and simply not shy away from an opportunity
• Learn from your mistakes. Add it to the list under "Wisdom Gained" and put that lesson into practice instead of making the same mistakes.

Now while you will note that "Having Sex" isn't listed, please feel free to the aooly first one when you do decide to have sex.

Based on your long history of lovelorn questions, and the obvious social naïveté that spawned them, it is clear a) that your friend is right about you; and, b) why you are still a virgin.

We can only guess what you are like in person, but as Tom suggests, the low assessment of your maturity may be based in a more immediate impression than the sum of your romantic inadequacies.

This, to me, is laid bare by the essence of your query here: That you lack a reasonable grasp of what qualifies as manhood. 

At 24, your frontal lobe is mature, your bones are fully grown and you should be at your physical peak.                       (Cue the trumpets)

What then have you been doing in terms of your intellectual and social development for the last 6, 8, 10 years?

Therein, I submit, lies the primary issue with your confusion. You can only blame your parents for your shortcomings for so long. So, you either take the drivers seat of your life and assume control, or you don’t. It’s on you now, and the clock is ticking.

To address your Q directly, my answer is this:

You are a man when you know who and what you are, can admit your faults, show due respect for yourself and other people, and carry your own weight in this world.

Take care of these, and the rest may fall into place.

You're virgin? You are a virgin. Raising has no relevance and more so being a man has nothing to do with sex. If your girlfriend doesn't want to go with you is fine. Sooner or later somebody else will. But you don't have to keep advertising you are a virgin.