forty_three
Stance: Goofy
It's definitely more common with goalies. Hasek was a backup until he was something like 28. Tim Thomas was a backup and/or minor leaguer until he was 32 or 33.
Those are certainly unusual examples, but it definitely shows it's possible.
Goaltending is more about mental development than it is physical development. Everyone has different places they can get to mentally, and differing paths to get there so it's natural it would take some guys a while (and why ome guys come out of the gate like mad). It's not as easy as figuring out which muscle groups to work when to make you skate faster or shoot harder.
You could have a guy who is physically gifted and an amazing athlete, but if he still flinches when a slapshot is fired, he's going to be shit in goal.