I was around a NW 3a and 41 years when i had my first HT of approx 800 grafts. My father had mostly a full head of hair in his early 60's so I assumed most of my hairloss had run it's course and this would be my only HT. My 2nd HT of 700 grafts was needed a couple years later to fill in between the transplanted hairline and further recession that continued. These HT's were NOT done by a coalition doctor and i was given an impression back then that my first HT would be it. They even seemed surprised(?) when i came back after the first HT with further recession and a gap behind my hairline.
Knowing what i know now, I'm surprised they did not consider this nor advise me of this possibility.
My 3rd HT was done by Rahal and he did a thorough job of explaining all the implications, present and future. Dr. Rahal also went back to my mid scalp to add some density as i was also starting to have diffuse thinning on top. He gave me approx 2500 graphs about 4 years ago and i haven't noticed any increased hairloss since. Still, I may need to go back again as hairloss is progressive. Meaning, unless you lose most of it early on, you likely could continue to have thinning in your 40's, 50's, 60's and beyond. Maybe you won't care by then, maybe, but just consider it.
FYI, my youngest brother lost most of his hair on top in his early 20's. My oldest brother didn't start having diffuse thinning on top until his early 40's and another brother only started seeing some thinning in his temples and crown in his late 40's. That's quite a range of hairloss timelines among brothers so be careful with any assumptions made about future hairloss.
This is why i personally would not consider a HT until my hairloss went beyond a certain NW stage, and not simply based on my age and an educated guess as to future hairloss.
Having said that, it's tough holding back when the hairline starts receding. Just make sure you use a knowledgeable HT surgeon and be prepared for additional work down the road.
I don't intend to offend anyone who has already made the decision. I just want to provide additional thoughts to consider.