well, wait till you guys are already having a conversation. Don’t just randomly say that out of the blue. That’s weird. The next time you guys talk just casually throw it in there. OR if your birthday is close, or even if it isn’t if he asks you what you’re doing or something, you can be like “looking at things to do for my birthday” (even though you’re not really doing that), be like “im thinking about doing so and so” and then he’ll comment like “ohhh that’s cool” AND THEN YOU CAN KILL TWO BIRDS WITH ONE STONE AND INVITE HIM TO YOUR FICTIONAL BIRTHDAY PARTY/EVENT and after you guys will talk about that for a couple minutes then you can be like “so, whens your birthday?”
There’s so many ways to go, girl and/or boy
you should’ve asked him when you asked how old he was!
But anyway, just ask! I don’t think that’s weird, i’m sure he won’t either. What are you worried about him saying/thinking? Or you could just flat out ask him what his sign is. It’s not a big deal, don’t worry.