Crackpot theory:

If Vincent is eternal (best name for his condition that i read yet), and he doesnt age, Then it is possible his cells dont age either. This could account for why he didnt have to eat while asleep for 30 years (lets assume he was actually asleep for that long).

Explination:

(Disclaimer: This explination may seem slightly inacurate, but I do it in hopes of making it more understandable)
After the human body has finished all of its growth phases, It stays at a constant state. Cells are still seperating and creating new ones. Not a rate suitable for growth but a rate that sustains the body. In fact after this point your body rarely starts producing large quantity of cells short of a healing process. A body grows old as the splitting cells that make up the various parts of the body age themselves (everything wears down). Thus, even when they continue to split they are splitting into aged cells which are not as good as the original young healthy cells that made up the body. After a certain point a cell dies, it is replaced by the replication of others. As stated before, however the replicating cells are also aged to begin with. this creates the downward spiral we call aging. All that having been explained, Vincents cells may no longer have aged, If they werent aging they may not have been dying, atleast not a noticeable rate. In this situation he would retain his youthfull appearance. Now (back in the aging world) as cells replicate they need a constant source of materials and energy (Matter cant come from nothing) We ingest food, both as a source for materials and to convert it into energy. Vincent no longer being restrained by the rules, could conceivably go long periods without eating. More so if he was asleep the whole time when the body is in a even more reccesive state.

Anyway, after that long boring explination that wasnt really neccesary, I feel its important to end on A high note: "One by one the penguins steal my sanity!"