I thought I'd posted, but it looks like it didn't go through.
I'd say share it with him early on, before either of you get too attached. When it's clear that you are starting a 'romantic relationship', I think that's the right time. If he doesn't want to date or marry a non-virgin, that is his right. And if that is a non-negotiable criteria for him, then getting deeper and deeper into a dating relationship could lead to a lot of pain for him (and you) if you wait too long to tell him. For some men, marrying a virgin is a big deal, and for others it isn't. If he's abstained from fornication, that doesn't mean he feels like he has to marry a virgin. But if he does, that is his right.
Something to keep in mind is that passage in the Old Testament where the husband gives the father-in-law the dowry of a brideprice for virgins to marry his daughter, but the daughter is not a virgin. When she is discovered, the law is that she be put to death. She'd played the harlot in her father's house. But notice there is not a death penalty for fornication in the passage about the seduction of a virgin. There is also an issue of fraud in the case of the woman who is married off as a virgin and is not one. She doesn't tell the potential groom that she is not a virgin. She most likely hasn't told her father and allows him to marry her off as a virgin. She not only fornicated, but she also deceived her future husband by her silence about the issue. Definitely don't let the man propose before telling him.
You probably don't want to go around telling your male friends that you are not a virgin. You'd want to know the man is interested in you. You could do this subtly by letting the man know that you'd fallen into sin in past relationships, or that past relationships have led you to sin, and you want to avoid that in this relationship. If he backs off in the relationship based on that, that's up to him. He may hint around for more details if he is the type who wants to marry a virgin, and you can see what he is hinting at and just tell him you aren't a virgin.
If he's fine with that, then you can continue the relationship. If he decides to pursue a relationship knowing upfront, that's his choice. If you wait until late in the relatonship, he may feel conflicted, like you reeled him in emotionally before dropping the bomb on him. Even if he were to propose later, that could still not sit well with him. If he knows early on, IMO, that is the more loving thing to do. If the topic of marriage starts to come up, you should definitely let him know.
I know a lot of posters say virginity doesn't matter that much. It might not to them. You aren't dating them. If the man you are dating tells you up front he doesn't care, you may not need to rush as fast to tell him. I'm writing from the perspective of a man who did care. I waited until I got married at 27 to have sex, and I wanted to marry a virgin. I got that desire while reading the Biblical teachings about virginity, and it was just something I definitely wanted. In my early 20's, there was a young woman I knew who was attracted, sweet, and I could see that we could really connect well emotionally, but I knew she wasn't a virgin, so I purposely kept our relationship a friendship. Later on, I briefly dated a woman, and a few weeks into it, I found out she wasn't a virgin. I'd been having this feeling my will power was the only thing keeping us from fornication and that she wouldn't have put up resistence. I broke up with her partly because I wanted to marry a virgin, and partly because I felt like the relationship was dangerous and could tempt me to sin. Non-virgins were not in my consideration set for marriage. Some peopel think that is awful, but these same people will say they had to marry someone thin, tall, a red head, a blonde, long-legged, funny, artistic, musical, full of charisma, etc. They had their criteria, which wasn't even related to anything in the Bible.
The good news is that not every man has the same criteria. And God is a good and generous God. I'm sure He has a husband for you. Do what's right by this man and trust the Lord. If the man isn't interested after that, accept that and trust the Lord. If it doesn't matter to Him, still trust the Lord.