I went to a hair transplant surgeon a little while back and he told me in most cases the most significant hair loss happens between the ages of 25 and 35. Is that correct?

that is certainly true in my case, and prob mosr i've read so i would have to agree, but you will hear of people as early as 16-18, and people as late into their 30's

The greatest loss came between 35-40... but I started thinning in my mid/late-20's.

Mr. T