Believe me, I'm not a big fan of some of what goes on with young kids and sex these days; but, respectfully, I think 24 is kind of being ridiculous. I see the sense in what the questioner is saying, but young people who are reasonably mature usually know ways to make good and sure no "accident" happens. To me, a nineteen-year-old knows as much about the importance of not letting an accident happen as a married twenty-nine-year old who has two babies under two, only one bedroom for them, and just enough money to pay the rent or mortgage and buy food.
To me, hoping to convince them to wait until they're at least out of high school (usually 18) and more mature than they are earlier than that was always kind of my aim. I always then figured that if someone ended up not quite making it to 18, that was better than saying, "Feel free at fourteen/fifteen."
My suggestion to all three of them was that I hoped they'd wait until they were in a relationship that was reasonably serious and long-term. In this day and age, I think that, in itself, is wiser than what a lot of other young people do. Also, to me, that was an idea they could (if they wanted to) bring with them into their twenties, thirties, whenever (if they were single).
I don't know... It's always a matter of trying to find that balance between hoping they'll listen when it comes being sensible and safe, but also living in the reality of how things really tend to go on (especially if they have a girlfriend or boyfriend).