Yes it's his magic that keeps him form aging.
So hundreds of years passed before he even met Regina.
I think the rest of FTL people age normally unless they are also touched by magic.
However I believe the blue fairy went said Bae traveled through a portal of space and Time so I agree with Rumple
Rumple/Gold is a smart guy so I doubt he would think August was his son if he knew it would be impossible for Baelfire to still be alive after hundreds of years.