Well to get an egg you need to take at least 256 steps. but its not always guaranteed.
The old man when he says. " the two seem to get along very well" means you have a 70% chance to get an egg and its 88% if you have an oval charm.
When he says "the two get along" its 50% 80% with charm.
The two don't reallt seem to like each other very much" 20% 40% with charm.
and The two prefer to play with other pokemon more than with each other" is 0%
@Earl is right its not 511 my bad.