An almost 47-year old Brad Pitt continues to keep his remarkably full hairline. As most people know, the hair loss risk increases with age ... But, specifically, at his age, Mr. Pitt is defying a 40- to 50-percent chance of hair loss.
It's my guess that Mr. Pitt has been very proactive in protecting his hairline over the last 10 to 20 years, and probably uses some type of preventative treatment - like FDA approved Propecia. I also wouldn't be surprised if he's used Rogaine from time to time (although treatment should be consistent to be effective) and low level laser therapy.
Just a hunch, but hair as good as his usually requires medical intervention.
But will it last forever? Not without medical treatments like the ones I described above.