Am i going bald? Only 18

[Occulus]

The brother (the only one) of my mother is bald and 4 of the 5 brothers of my mother's side grandmother are bald BUT both of my grandfathers died with full head of hair and my father has very good amount of hair at 50 (he started losing a little at ~45)
The thing that worries me is that my cousins (sons of my mother's brother) have some serious receded hairline at 21 and 18

All of that is meaningless; it doesn't matter if your father and grandfathers and cousins have full heads of hair - you can still go bald. Conversely, every male on both side of your family could be bald, and you could keep your hair. There is no 1-to-1 relationship with genetic baldness and family history.

Yes, it looks like you are in the early stages of hair loss. You have recession at the temples in a classic NW1.5 pattern. Go see a dermatologist, then get a prescription for finasteride. If minoxodil is available over-the-counter, get on that, too. The earlier you catch it, the more hair you'll keep. Luckily for you, it looks like some good therapies will be available in the 5-10 year timeframe, so even if you lose a lot of hair, you'll probably be able to get it back by the time you're in your late 20's.

[valiattims]

And there are some short hair falling (~3cm)

[Thinning87]

When it's wet, it seems to me that there might be some very early stage thinning on your temples, which would mean you will lose your hair throughout your 20's. It's most likely the pattern of someone who has somewhat slow loss, and will look like he has a full head of hair until around age 24. Then the thinning will become observable at around 25-26 on your temples, and you will have to start wearing your hair short after 27.

I could be wrong, you need to go see a dermatologist. Only a professional will be able to tell you, definitely don't take anyone's word on a forum.
Lucky for you, if you are in fact losing your hair, our recent news confirm that there are 2-3 companies out there with products that have amazing potential, and if you will be able to afford them, by the time you are 24 there will be something out there and it'll be like you don't have hair loss.

[Hairmore]

All of that is meaningless; it doesn't matter if your father and grandfathers and cousins have full heads of hair - you can still go bald. Conversely, every male on both side of your family could be bald, and you could keep your hair. There is no 1-to-1 relationship with genetic baldness and family history.

There may not be a 1 to 1 relationship between the hair status of your relatives and you, but there certainly is some sort of relationship. I do not want to quote any scientific papers here but the relationship is apparent when I look at my relatives and some of my friends. I have never see a guy going bald with his parents and brothers still with a full head of hair. My bros also have mpb.

[Hubris]

There may not be a 1 to 1 relationship between the hair status of your relatives and you, but there certainly is some sort of relationship. I do not want to quote any scientific papers here but the relationship is apparent when I look at my relatives and some of my friends. I have never see a guy going bald with his parents and brothers still with a full head of hair. My bros also have mpb.

I agree with you, but I must say that there is only one person in my family who lost his hair around the same time as me (17 onwards) and that would be my uncle on my father's side. My grandfather is 74 and only started diffuse thinning about 2 years ago, and my father is in his 50's and only has the slightest recession now.

[Hairmore]

Hubris, similar story with me. My father is in his mid 60s and only started to really thin now. My uncle on my fathers side started to thin a long time ago (probably in his early 40s). On my mothers side there is not much hair loss going on and my brother is thinning a bit slower than me. Both my grandfathers were started to thin some time in their lifes but I have no clue how strong it was overall.