mice are not humans, you don't think that a 60-year-old man will go back to his 20-year-old ageI wouldn't say it's always a necessity to start longevity experiments on infants only. We've already seen how some aging can be reversed in grown mice by injecting them with stem cells found in the embryo of mice. So who knows, maybe they might use a similar technique.
Regarding the Balding, it seems as if they simply are not concerned with hair. Surely they know they could atleast go for SMP, a hair system, hair transplants, etc but they haven't. Probably because they, like The Rock, Dwayne Johnson, consider themselves better looking without hair.
But once the longevity tech comes along, I doubt it wouldn't be of interest to them to indirectly regrow their hair because one of the methods they also seem to be experimenting with is returning cells to a younger state. By doing such they may be able to turn the cells in the scalp, back in time to a point they weren't sensitive to DHT and hairloss and back to a growth phase.
Who knows, if their successful at re-triggering growth phases in the body, they might even eventually in the distant future be able to create more growth in humans than humans were previously bio-genetically limited to, possibly being able to alter/increase things like height, etc.