Does Wifi P2P require *both* android devices to be 4.0+?
"Normal WiFi" and "WiFi direct" are separate things. If you want to use the latter, the answer is yes: both devices must be supporting it. If, on the other hand, your question is whether there's a way to directly connect the two: there's always the "hotspot" feature, which was introduced already before 4.0. So one device (supporting this) could act as a WiFi hotspot, and the other could connect there as to any other WiFi router.