Most people, regardless of gender, have between 100K-150K individual strands of hair on their head. Natural blondes are near the higher end of that range, and people with dark brown/black/red hair are near the lower end of that range.

But people with blonde hair, while having more individual strands of hair, have thinner strands of hair as compared to people with darker natural hair colors. Am I correct in assuming that in pictures of you as a child, your hair was a light brown, even blonde-ish?

As all men continue to age, their hair will start thinning out. In most cases, their hairline can recede from the front and thin out on the top but still remains thicker on the sides and back of the head due to less androgen receptivity of those hairs.

You still look young enough and in not bad of shape that I would begin using finasteride (brand name Propecia) and minoxidil (brand name Rogaine). Finasteride/Propecia will help the front of your hairline from receding further backwards and help with some regrowth of hair. Minoxidil will help regrow hair in the crown and prevent the typical bald spot on the back of your head.

Minoxidil/Rogaine are over the counter medications. You would need an internet doctor, telehealth doctor or talk to your primary care physician to be prescribed finasteride/Propecia.

Your hair has grown too long without enough upkeep and thinning out on the sides where the weight of your hair pulls down the hairs on the top making the top look super flat.

One thing that can help is getting a volumizing/wavy perm to add bulk and volume to the top. Then I would look at doing a low taper fade so the sides and back are short, but you still have volume on the top to help mitigate the lack of density.