Zombies can be any age.

Neutral Evil: Zombies only care about their next meal!

The adult human can be 5-6+ ft tall.

Your base walking speed is 20ft, swimming speed is 10ft, climb speed is 5ft, and burrow speed is 5ft.

Your teeth are natural weapons, which you can use to make melee weapon attacks. If you hit with them, you deal piercing damage equal to 1d6 + your Strength modifier.  If the target is a Medium or smaller creature, it is grappled (escape DC 13). Until this grapple ends, the target is restrained, and the zombie can't bite another target.

A dead creature previously infected by a zombie comes back to life under the zombies control at one fourth its max hit point value. An infected creature is a creature who has been scathed by this kind of zombie or has ingested zombie blood in some way. 

Your nails are natural weapons, which you can use to make unarmed strikes. If you hit with them, you deal Necrotic damage equal to 1d4 + your Strength modifier, instead of the bludgeoning damage normal for an unarmed strike.