Time passes. Well before Zeus's thirteenth birthday, he looks human-25, and then he stops, and Harley catches up; Zeus is still taller, but not by much, and burlier, but not by much.
Wolves have a lot of casual sex amongst themselves; the girl wolves can't get pregnant, and with pack telepathy it would be pretty hard to hide a secret crush. Everyone avoids getting serious - well, the lesbians don't, but any couple involving a male wolf has to avoid deep emotional entanglements that would shatter if he imprinted; the Imperial Seer helps, but she is not perfect and they will live for long enough that even a slim chance adds up. But casual sex absolutely happens. Zeus has a friend with benefits by the time he's fifteen (her name is Kitty, but she thinks this is ridiculous, and prefers "Xanthe" after her yellow fur).
He helpfully passes on to the pack that Harley thinks they are all hot; several people take advantage of this information, and Harley has more than one friend with benefits at the age of fifteen.
(Meanwhile, the masquerade is in tatters; wolves are just more convenient than looking for human partners, at least until Zeus decides he's interested in the Seer finding him a suitable imprint.)
This newfound interest does not mean Zeus and Harley don't hang out, even now that they're both sixteen. Presently, Harley is getting his ass handed to him by his wolf-reflexed sparring partner at a mo-cap fighting video game entitled Bloodsport V.