The key to becoming a Mason is really tricky.......you have to ask to join. In the past it was considered strictly forbidden for a Mason to ask another to join, as it was supposed to be of his own free will and accord. Many Masons took that to mean that they could not discuss membership at all.
This is no longer the case and most Masons will be glad to discuss Masonery and it's benefits and obligations to anyone who asks.
The other requirement is that you profess a belief in a higher being. (In my case, God.) You are not required nor encouraged to discuss your particular beliefs beyond this however.
Hope this helps, and I would encourage you to talk more to your grandfather.....you may find some pretty amazing things!
I'm going to ask him about it more.
He's probably one of those old-school Mason's (he's 90) and doesn't bring it up. EVER. But he's got a really big ring and he travels all over the place for meetings.