Men often inherit hair loss. Young hair loss usually start at the front and worksback across the top of the head. Hair thinning and loss for men as they age usually start at the back top of the head and then thins all over, the top of the head most noticeable. Men can have either, or hormonal loss, or loss can be caused by infections also on the scalp.
Women tend to have hormonal loss, but also can inherit hair loss or have an infection. My thyroid being difficult to regulate causes tons of hair loss all over my head, most noticeable at my part, because at the top of your head there are not layers of hair to mask the loss as well. Once I adjust my medicine the hair starts growing back in again.
I have read that iron is important for hair growth. I think there is no concrete proof of it though. I do struggle to keep my iron in normal ranges. Also, many people say biotin helps a lot.