As always, the problem is not sex, but causes and consequences:
(a) pregnancy – and the damage this does to not only you, the child, but the society that must pay for your mistakes,
(b) and single motherhood,
(c) or immature parenthood,
(d) the degree of interest in it, such that it detracts from other things.
(e) the high correlation between multiple sex partners and unsuccessful families.
The ‘intensity’ of the male sex drive in the teens is just …. amazing. Testosterone is the most wonderful drug of all. It’s just mind-consuming.
I think for boys it doesn’t matter – we are evolutionary machines and the need for sex is purely physical. But girls are different – and should not use sex to ‘buy’ attention, or being liked, or ‘belonging’, or ‘status’ (which is all too common), and should not participate because of alcohol or drugs – if you need alcohol you aren’t ready yet.
This is the best test: If you aren’t prepared with protection, aren’t ready to do it without chemical assistance, aren’t willing to plan it rather than stumble into it, and you aren’t willing to keep it between the two of you permanently, then you aren’t ready. Conversely, if you have protection, don’t need chemical assistance (drugs or alcohol), can plan it so that it’s private somewhere, and can keep it between the two of you permanently (the urge to tell everyone is very powerful), then you might be ready.
General rule of thumb: What happens between male and female is no one’s business as long as you don’t make it anyone’s business. This is true in all walks of life. The problem is, do you need to tell anyone? If you do, then you aren’t ready.