Gandalf's comment about Frodo

[Lotrelf]

Originally Posted by Inziladun

I'm sure the mental strain of constantly resisting the Ring contributed to Frodo's appearance. He had probably been gradually aging in that way since setting out on the Quest, as the Ring's power grew along with Sauron's (and it's growing proximity to Mordor as Frodo and Sam traveled). As in real life, gradual changes often go unnoticed until one has an "aha" moment where life allows a momentary stillness, and time for one to really see something.

How? After getting the Ring, Bilbo stopped aging; Gollum lived for more than 500 years. This means: They stopped aging. Why would Frodo look old, then.? He had stopped aging as well, as we are told in FOTR. Or we are saying the same thing, his "growing wisdom", but differently?