Given that our 17 year old, six foot tall male or the "man in question does not age nor does anything else." From this assumption all else follows, he will need to eat no food whatsoever. Why? You may cry!
He isn't changing or ageing or apparently undergoing any of the usual changes a normal human being might undergo. This is a world where miraculously everything is kept in a state of perfect preservation. Presumably he will only eat from habit, but considering he also won't to perform the usual comfort stops as well. In which case, eating more food might become a problem for him.
Unless, of course, he needs to consume food to provide the chemical energy needed to power his metabolism and move around. Quite possibly if he sits still and doesn't nothing this won't be an energy cost since he like everything else is perfectly preserved.
But calculations in other answers reveal his consumption of food over a quadrillion years will vastly outweight his needs. This little problem might be resolved not so much by growing more food or importing it from other universes, but as a beneficial side-effect of the perfect preservation process (PPP).
If the PPP not only preserves the food (and everything else) it also is capable of restoring matter and objects back to the way they were after being affected by an uncontrollable change event. For example, having a meteorite crash into a warehouse full of food or a 17 year old, six foot male eat it. The PPP will restore the food filled warehouse back to being a food filled warehouse and not a large crater. Ditto for the food the 17 year old immortal shoves down his gullet.
This does mean it is now irrelevant how much he eats, because there will always be food around for him to eat. Also, he doesn't need to rove around the planet looking for food.