Well back in the day when everybody was converting to Christianity, children did convert against permission of their parents, spouses did convert against permission of their spouses, etc. That’s why in the Bible Our Lord tells us to leave everything behind and follow him, even rebuking the man who just wanted to go bury his father first. It’s your call, but as long as you’re above the age of reason, this is your soul, and your decision, which is sad because your parents should have the well being of your soul on the top of their priorities, but I do understand why they are upset.
You just need to evaluate it from both sides… what if you did officially join the Church? Your home life might turn into hell. Could you handle this maturely and as a strong penance/sacrifice, and use it to grow even stronger, or would it frustrate and upset you, leading you into sin? BUT then you would be able to receive the Eucharist, receive God Himself into your own body, and have your heart one with His Most Sacred one.
To be honest if I were you (I’m 18 now, so I kind of get where you are in your relationship with your parents) I would secretly convert. You could deflect and not lie the way priests did during the Anglican Persecutions. Are you a Catholic priest? No, I am not a Catholic priest (under breath: who doesn’t say the rosary.) Plus, do you already attend Mass? Bingo

And even if confession is scheduled on Saturdays, you could arrange for the priest to hear your confession before Mass, and have him help you to keep this secret. I believe many saints did it this way, and when they were found out their own parents made them martyrs

I think you can handle less than that, right?
Let me repeat that the Church has NO LEGAL AGE LIMITS besides the age of reason. If you were in England they might say, well once you’re sixteen, and somewhere else they might say, when you’re twenty. Eighteen means
nothing where your soul is concerned.