It’s possible that the WOZ found a way to travel between our world and Oz more than once (i.e. has made many return trips). If so, then his aging might have been halted over the last few decades, since I think the curse froze all the lands with magic, if I’m not mistkaen.
True, that’s possible. Dunno if I’d like it though, because the basis for this show is the tragedy that Rumple’s only way to get to our world to find his son was to destroy a whole world. If it turns out he could have just gone to Oz and stolen the Wizard’s balloon, then that makes the lengths he went to for the Curse sort of ridiculous. He knew about the slippers, so by rights he should have also known about the balloon if that was possible.