If your hair has always been like that then why would you think your losing your hair? If your going bald you will know if your half way observant. Take pictures and compare them a year later its usually a slow process so you have plenty of time to catch any changes before they get big. The best indicator is family history, but even that is not foolproof. From the picture if your hair was like that then I dont see anything wrong, but a derm looking in person would be a better person to see if your worried. I dont buy into the mature hairline theories I say if you see hair missing where it was before then your balding.