I remember first noticing my hair loss and it was when my widow peaks were exactly like that.
It might be the very start of male pattern baldness. It might also just be a maturing hair line. Most men do not have a straight hairline all of their lives. Some men lose the spots around the temples (the temples are so weak) and it never really progresses further. I would really just keep an eye on it and see how it develops. I remember when I first noticed some signs of losing hair, I immediately thought I'd be slick bald by 30. I'm 30 and I still have great hair.
If you're concerned about this and want to be actionable, there's not a lot to do at your age and there's nothing really worth trying to do (medically) at this super super very early stage. Eat healthy with lots of nuts and plants (getting vitamin E is good), no processed meats or refined carbs, brush your teeth, don't smoke. Don't go too hard at the gym. Are you taking creatine? If so I would stop that.
Go see a derm when you're 18.
