17 yo relationship ?

As long as you're over 15 or so, relationships are fine, fun and will help you learn useful things for later on in life.
Anything before that is just excessive, and relationships that start there usually end far before they can actually get serious.

If you're planning on doing something sexually before 17/18, then you need to rethink things because if you mess up, that's both you and her fucked lmao
IMO sex is overrated, if you're doing it because someone really loves you and you enjoy spending time around them, then sure, go for a relationship before 17 or so, it's not going to do anything other than help you learn from the experience.