Teenage son - girlfriends????

I had this conversation with my teenage son (15 years old) about girlfriends not long ago. I told him that now a days children or rather teenagers start to fall in love even though they are only 12years old. Falling in love at such a young age could sometimes be term as Puppy Love, Adolescent Love or Infatuation. He was asking me whether having a girlfriend is OK. The answer is definitely NO, as I try to answer him with whatever reasons I can think off. I always remind my children not to fall in love so very young (talking through experience) LOL. Once you start to get involve (fall in love) it will affect your studies and mess things up (emotionally). If there is a argument/ quarrel between the pair it would be the worst nightmare. I always stress the important of studies first and love will come automatically if one's is successful, especially to my son. As for my daughter she is more into taking my advice but kind of cheeky in a way. I always advice my son if he wants to fall in love with a gal. He must be at least in university and find a gal who is at least 5 years his junior (10 years would be better). So one day he asked me why the need for age difference. I told him that girls aged faster than guys in their sexual desires. This is a fact and from getting feedback from many couples who are married. Even my father once told me that I was not sure I believe him then but now I do. The most important thing is to stress to my kids not to fall in love for the time being (when they are still schooling). If they want to mess up their life now then what can I do, I can just do what a dad has to do advice and advice( I think I am not nagging) and hope my kids will listen to at least some of it and come to their senses. I have to wait for a few years to see my wishes come true for me and my children. I sincerely hope they will listen to my advice. What advice would you give your children if they come up and say that they have a boyfriend/girlfriend or say they are in love at such age?