That is a ridiculous anti-biological solution.
Honestly, I don't have a good solution but I do know that people used to start having kids at much younger ages when they were in hunter/gatherer societies and even up to 100+ years ago young people were able to support themselves and start a family.
It's only been in the last 100+ years that we have been essentially forcing people to continue their education until they are 22+ and thus not be able to support themselves and a family.
Of course, we have a lot more information to learn and ways to specialize nowadays, so again I don't know what the best solution is but to try and convince a 17 year old or 18 year old not to have sex is retarded. Some of them will be fine with it, but for the majority it just isn't going to happen.
Fortunately there are better birth control methods out nowadays that have been able to help mitigate this issue, and of course abortion being legal and generally available does as well even though some people disagree with the moral implications.. That would just mean it is more important to teach and help rely on better birth control methods, or else try and educate young people with more applicable skills so they can get more lucrative jobs sooner.