It's difficult to know without more specifics of why he got the full-time position. It's a great accomplishment for him but his app didn't sound as technically

It's difficult to know without more specifics of why he got the full-time position. It's a great accomplishment for him but his app didn't sound as technically rigorous as the interview or job requirements Facebook would give a 30-something. It's probably the same reason the news finds teenagers passing college calculus/physics fascinating but not so with 30 year olds. His app could have also solved a lot of technical problems that 30 year olds couldn't in interviews and maybe he blew through Facebook's technical interviews easily.