Underage relationship

Im reading all these comments about how everyone is saying how they had sex at a young age (13-17) and they regretted it. Im contemplating it and I want to know why it was a bad idea. My boyfriend and I’s relationship isn’t bad at all and we work so well together. I understand that its a young age to do any of it but we truly love each other and we both think its going to last. I just need a bit of guidance.