Literally all those questions have been answered and studied by scientist and educators. No it’s not a concensus answer but they mainly state, “You should give comprehensive sex education once puberty starts. (smaller more age appropriate conversations should be had about sex throughout a child’s development) With an emphasis on absence as the safest way to avoid pregnancy, STDs and emotional harm. Respectful monitoring of teenagers activities and open access to contraception.” (we’ve all mostly been there. With all the hormones and changes teens bodies are telling them to do something they are not fully mentally or physically able to do safely.)
Not everyone physically or mentally develop at the same rate and purely scientific measuring teens naturally should be experimenting with each other in some form of sexual contact until early adulthood. In which more emotional bounds are formed. Ideally women shouldn’t be having kids until they are around 25 years old. Mentally and physically that’s when their body is truly developed and ready to give offspring and themselves the best chances at survival.
Comprehensive sex education covers abstinence. Yes you cover safe sex and iud contraception. Yes, religion has ruined what the perception of abstinence, but that doesn’t change the fact that abstaining is the safest way to prevent pregnancy, stds, and emotional harm. I actually taught sex Ed for 5 years. Ideally teens should only engage in none fluid exchanging sexual activities until early adulthood. I would always joke with my students that “I’m not here to tell you, ‘don’t have sex or else you’ll get pregnant, die, and/or go to hell’ If you are going to have sex please explore other options first, than use contraception if you must. But abstaining is the safest option.”
I also only had religious based sex education where the told the girls in my class sex was like a piece of tape. The more you use it the weaker the bonds you have with partners and God. Soooooo Ya needless to say my graduating class all were pretty much fucking every other day. Absurdity in learning never leads to good outcomes, but honesty will always win out. Abstinence should always be the preference but not the only option, with full on no contraception sex should only been done once you are fully developed and mentally able to take on any consequences of your actions.