Yeah I have thought about this one too, I guess I am paranoid about it (would like ugly without the hair!)
I'm 26 in a couple of months, in the past maybe 3 years I have thinned about (this is an inaccurate wild guess!) 30%, from having a very thick head of hear.
I still have complete coverage, but my parting line has just stared to widen a little at the front and looks whiter, also on my parting there is a patch of hair that it only about an inch tall? the rest is very long. My hair has always been a bit diffuse at the very front, but cause this has happened it looks like i'm thinning over my parting unless I put a bit of cream on to hold it down in place better, give it some weight.
my overall scalp is a bit diffused. my parents have this at 50, worse than me but are not bald. My dad has quite a bit of thinning at the back now (he is mid 50's) both grandads we're bald as.
anyway, maybe I should wait some time before I start then, untill it gets worse.
some people say start it now! get it right where it starts cause it's harder to sort things out once you loose coverage, some people like this instance are saying start later and you'll have more years. I hear people saying that's how I started, by diffusing all over the scalp then bam.
some people say it looses it's efficiency, some people say there's no proof of that.
oh well, I don't know if I should start it or not. maybe I'll take some photo's for my reference now and wait a year, compare and decide then.
do some people diffuse and never go bald?