Because destiny had a different plan. They were supposed to meet later. People come into our lives at certain times for various reasons having to do with lessons to be learned. It is not a coincidence that they didn't meet at a much earlier age when they did not have other commitments. I think the reason people meet later is to learn about love in many different ways and about how to balance this with responsibility and commitment. They'll meet again in a different lifetime. They must be patient.