Basically, once you have a proper vocabulary when you can talk and have a conversation. Oh and you can walk/run.
That's the time you should start school.
Oh Jesus, that means I'd start school at around 1 or 2. Now no, they weren't understandable conversations on the the intellectual level, but they were good enough to go to preschool. So having said, I would now be in the... freshman year of collage... at 15... holy snarks. I like this system idea.
Teenage dates last so short.
4 months and going strong, plus to add to what Colten said:
My sister met my brother-in-law in 6th grade. They started dating, and they've been together since. Now they're married and have two kids.
My cousin's both started dating there Husbands at my age, they are now married and have kids. Freaky world isn't it.