My hair started thinning when I was 23 years old, so I've had plenty of time to get used to it! I trim it once a week with the shortest setting on my beard trimmers, it makes life so easy.
My 29 year old son has a full head of thick hair but my 27 year old son has been thinning for a few years so it's not all genetic (my Dad had plenty of hair until the day he died).
