J19C
I would not consider your hair loss pattern/potential future hairloss based on your siblings. Male pattern baldness can escape generations.
If i were 19 and in a similar position to you (friends noticing your hair is thinning) then i would start using Rogaine immediately (its £25 for a 3mth supply of the liquid or £40 for a 3mth supply of the foam, the foam drys in 5 minutes). In 3-4 months time your hair could really thicken up and go back to where it was 2 years ago.
Finasteride is about £45 for a 3month supply. This drug can maintain your hair and stop further loss, it has maintained my hair for 20 years. Get on google and do some research and make an informed decision if its for you.
Finally if you are destined to be bald completely by your mid 20’s or have an advanced hair loss pattern. You only have a limited number of grafts for a hair transplant. Let’s say you have 5000 grafts, that is typically 12000 hairs that is nowhere near enough to keep your head warm in winter and would give an overall thin look. If they bodge the hair transplant and you only get 50% growth then there is no return from that. This is why you need to do all you can to maintain your existing hair.
If you want to hide the thinning appearance of your hair, buy some Toppik. But remember less is best and only do a light dusting otherwise it will look fake.
Good luck.