(Answers.com)

You’re the First Real Girlfriend
if he had a girlfriend or two in high school, but hasn’t had a real girlfriend since that time, you can bet you’re dealing with a boy who is going to need help with the basics. He isn’t going to know how to properly act in a lot of scenarios, and you’ll be the one teaching him. Prepare yourself, or consider moving on.

He Lacks Communication Skills
This is a big deal, as all relationships are founded on the ability to be able to communicate. If he shies away from talking about anything, it may be a sign that he doesn’t know how to communicate. If this cannot be overcome early in the relationship, you might consider bailing before it’s too late. Once this pattern is set, it is difficult to break. His lack of communication when big issues arise will only cause fight after fight after fight.

He Gets Lazy
If your relationship starts off as it should, with him putting in effort by asking you on dates, sending you flowers, and sending “thinking of you” texts, and that suddenly stops, you’re dealing with an immature guy.

He Plays the Blame-Game
It’s inevitable that people who care about one another will eventually fight. However, if your man is blaming you for everything and refusing to own any faults of his own, he’s not only immature, he’s also egotistical. Neither will satisfy someone looking for a mature relationship for very long.

He is overly self-conscious
If your guy is always worried about what other people think, you might be dealing with someone who isn’t very mature. In relationships, this usually shows itself when your guy won’t do certain things because he’s afraid that his friends will think he’s whipped. If he’s worried about being seen as whipped, he’s not concerned about you. Time to find a man who doesn’t care he looks silly or feminine or whatever.

He has a Disappearing Act
When things go wrong, a partner is supposed to be someone you can lean on. Everyone needs help at some point, and strong men are there for their women, just as strong women stand behind their men. However, if your man doesn’t want to be depended on and disappears when things get tough, you’re dealing with someone who hasn’t grown up yet.

He’s a Hypocrite
Everyone has things that irk them to no end, and when you discuss it with your partner, you expect him to meet you halfway. However, when your guy brings up things that supposedly bother him, but does the exact same things later, it’s understandable that you would be confused and a little annoyed. If your man doesn’t follow his own rules, you’re likely dealing with someone who is immature.

He’s a Jerk
If your boyfriend suddenly starts acting like a jerk to the point that you have to call it quits, you might be dealing with a guy who’s too chicken to break up with you and is pushing you to break up with him. A guy in this phase will not care that he hurt you, so it’s best to just move on. He hasn’t grown up, and this circles back to his inability to properly communicate.

He Seems Helpless
A real man knows how to take care of himself. He knows how to cook, clean up after himself, and do his own laundry. If your man is kind of helpless, especially when you’re around, it’s more likely you’re a mother replacement rather than a girlfriend, which seems creepy. The truth is, he’s not mature enough for a relationship.