Are you dating or marrying these people?
"Mates" sounds like you are on a mission for a spouse, which means you're are definately on the dating fast-track. It's your personal business but why the rush?
Obviously if it's someone you are going to marry - it will and should come up, in my opinion.
If you're just dating it's not like your opening line is, "Hello my name is JimBob and I'm a Libra, I like long walks on the beach, I value honesty, and by the way I used to be a Jehovah's Witness, but I'm not anymore, however I think I may have some hang-ups."
It usually comes up naturally in the conversation. It's not generally something that needs to be forced. Plus, to most "worldly" people - it's really not a big deal. They won't really understand why you're so worked up about it and feel the need to "lay it all out there".
Like I said, if you're just dating - you'll end up telling some people who inquire, or you just may not tell some of them at all, but if you're serious with someone and intend on marrying them - like I said - most likely it will come up at somepoint before you pop any questions about a forever-after with them, as it should.