Young wild mouse?

Hello. Today my indoor cats had been acting weird and 'guarding' our vents. After a few hours i discovered this lil guy near the font door playing dead. He doesnt appear to be injured from my cats (surprisingly). Took him a few hours to calm down and ive been feeding him oat water with a paintbrush.

Anyone know if this is a mouse? Or rat? What kind of mouse? Possibly how old? Anything i should watch out for disease wise? I was thinking of keeping him (despite being severely allegic) or rehoming him to a family member with rodents.