You should not be sending signals to your son about getting married at all. There are many reasons he may not want to get married right now or get married period.
1. Your son may be gay.
2. He may not have met anyone who seriously interests him.
3. He may have goals he wants to accomplish before he marries.
4. He may never want to get married. Many young people nowadays are choosing to remain single.
5. He may not feel he is in a position to get married right now - financially, emotionally, job security, savings, etc.
If you nag at your son to get married, he may feel pressured and marry someone he is not suited to. Let the young man make his own way on this one. If he asks your advice, give it. If he doesn't, don't.