Our son sailed with us throughout his whole life... 18 days old the first time. I'm happy to say that he's a boat owner himself now and sails/races on OPBs as well.
While he had no choice in the matter, really, especially early on, I think what tipped the balance was a few things we did along the way.
We designed and built a littly opti-like dinghy when he was 4 or 5 and he started sailing it on his own not long after. He learned to row in it too, and it provided hours of entertainmnet (and independance) as he was growing up on the water.
We started a small jr sailing program with a small keelboat and that got him and a bunch of his peers interested/involved.
When he was 10 we bought a small dayracer and after a nasty broach his mother was not so keen on sailing it anymore - we raced that boat for 6 or 7 years with myself, our boat partner, and our two boys both the same age. We had an active little local race program in our club in an area with fairly challenging conditions. After a season or two, we had a great thing going.. rarely were words required, our boat handling was almost automatic and we "ruled" for many consecutive years. I think this alone was the key to his continuing enthusiasm.
When the boys were 15 we started to get the usual teenage reluctance to go sailing with the parents. Since we owned two boats in our partnership we let the boys take the 24 footer - they invited friends - and we cruised the bigger boat. We kept the food stocks so to be sure they'd join up at the end of the day. We had a fabulous 3 week cruise that year and we had all kinds of space on the bigger boat since the kids lived on the smaller one.
When he went to college he listed on a web based crew list, got on with a local racing boat and has never looked back. His resume now includes time on a variety of boats including a Farr 40, TP 52 and most recently a couple of seasons on a Melges 32. During this time they bought a Ranger 29 and have recently moved up to a Catalina 36, and "scooped" us by having his daughter on the water at 1 week old!
Still, I'd say you're starting a bit late but wish you the best.. as you say you can't force them, but you can make the opportunities available, and encourage them the best you can.
Apologies for the parental bragging......