Fraternal twins, one lost crown hair 40% by HAIRCHECK the other did not, can you explain this?

I just turned 20 and recently started taking propecia as my doctor told me I have lost about 40 percent of my crown hair using haircheck (None of this is visible). Even I was surprised to learn that I was actually balding. There is baldness in my genes but it’s not really aggressive or noticeable until older age (40+). Additionally, my fraternal twin hasn’t gotten his hair check but I am assuming he has not lost any hair yet. I am currently on finasteride and planning to take it as long as possible if the side effects aren’t severe. Do you think it’s possible for me to keep a full head of hair (or the appearance of one) through at least my 30s? Thanks

The difference between frarternal twins may be related to stress but the genetics of one does not impact the genetics of the other. Did you have more stress in your life than your twin brother. Did you go on any radical weight loss diet?. These can be causes of bringing out the genetic in you and not your brother but maybe your brother did not inherit the balding. Taking finasteride might work for years, if you are one of the lucky ones.