You are a young man of 18, I think you have the ability to understand what is good and what is bad according to your age. You have known about Bitcoin since you were 16 years old hearing about it. If you have a good salary and are not dependent on parents, you can invest monthly or weekly using DCA method with part of your salary. But that's not all, you must be experienced with your investments and holding your investments. Everyone's parents believe like your parents because they are not of my generation like yours it will take time for them to understand about Bitcoin.
OP is very young and has good potential in managing everything, has learned to understand Bitcoin at the age of 16 and now at the age of 18 understands crypto and Investment we think he will be able to design all of this well, at this young age by getting a salary and being able to understand investment provides good opportunities and potential for him.
Yes, doing DCA in making his Investment should be the strategy that he will use to organize his Investment, either done every week or every month according to the provisions.