Originally Posted by
WilcoRoger
The only way you can earn miles for someone else's flights if you share the same name - possible scenario for a father-son duo.
True. But I think that's technically against most FFP's T&Cs, so at your own risk.
Would also potentially raise a flag and cause issues if father/son (or mother/daughter, sibling/sibling) were to ever travel together or on competing routes (e.g., someone boards a flight while other person is in-air) and try to share the FF#.