It has to be pure myth to state that Zeus put on 30 lbs. of muscle since arriving at the UA. Muscle cannot be built that quickly. The articles I've found referencing his weight gain simply state that he put on 30 lbs. of weight.
As far as the notion that he might be "physically maxed out" - not true. Athletes typically reach their peak between ages 25-35. To suggest Zeus has little or no upside left doesn't fit.
He'll be continuing to maximize his physical attributes and athletic abilities for many years to come.