Granted nobody probably cares and its probably insignificant but I wonder if there is some reason why the 3rd hokage wasn't resurrected in the form of the prime of his life. When madara was resurrected he came back in his prime and not in the old age he died in. Maybe orochimaru has no plans on using the hokage as his battle pawns so he didn't necessarily need him to be in peak battle condition, but it's hard to believe he'd pass up such an opportunity.
You're brought back based on the DNA retrieved from your body at the time. The only DNA Oro has of the 3rd is his aged self so yeah... no prime 3rd Hokage for us. Does it really matter though? He has unlimited chakra and the ability to not die so.. it's as if he's 20 again. With liver spots. Yeah.
I think Orochimaru at this point realizes he isn't stronger than a full-powered Madara or even Obito due to their Rinnegan and like a good snake is playing the field, waiting for an opportunity to strike.
Unlike the previous time he did Edo Tensei, I suspect he'll let the summons act on their own hedging his bets that if he allows them to run free it'll play into weakening an Uchiha long enough for him to snatch some eyes.