You've got a weird definition of old man, buddy.
You think being old enough to have kids who have kids isn't 'old man'?
You've got a weird definition yourself.
Nah, you become old at about 40, then you stay old till you're 90, then you die.
This has been true basically forever. Every new advancement that extends people's lives doesn't slow ageing, it just lets you remain alive as an old person for longer.
... granted, people in Avatar regularly live to be 100+, but 50 is still too old to be boning teenagers.
Not for ethical or legal reasons, but just because it's not hot anymore.
Leave it to the 20-something studs.