Welcome! And I think it's great that you're working on this when you're still so young. Lots of us were not so fortunate (or so wise!)
About your parents' concerns, whether you might start too soon and regret it-- I won't lie, some people do. And, from what I've seen the ones that start early are a little more likely to regret it. But the vast majority of trans folks don't regret it, and wish they'd started earlier. It's also worth remembering that, just because someone regrets a decision, doesn't necessarily mean that they should have made a different one. Nobody knows what life would be like if they made different choices. Part of the reason people who transition later are less likely to regret it is that years of dysphoria have showed them what the alternative is. If you transition early, you don't risk spending part of your adulthood living with gender dysphoria. But that also means you might underestimate how bad it would have been.
There's a price for waiting, too. Some of that price is social or emotional, but some of it's also biological. Physical transition is harder the older you get, though trans guys have it easier in this respect than trans women do. Even if you don't start T for a while yet, there are things that can make your body better prepared for it.
A gender therapist would almost certainly be glad to talk with your parents and you together, to help them understand what you're going through. I'd also recommend you think of therapy as being something you can do to help your transition, instead of just something you can do to get T. Growing up trans is hard, and we've all got some baggage that we could use some help in dealing with. And, on the off chance that you're someone who might regret transitioning (like I said, not likely, but still worth keeping in mind), therapy can head this off.
Welcome and good luck!
