22 year old female horse and 21 year old male ram

Do you mean ram or rat?
If it is a rat, I am afraid that it may not be a good pair. They are totally different on how to make their relationship going on. Rat like chummy life but horse want independence. Too much attention will make horse feel uncomfortable. When this problem come out, both of them will want to get rid of it and want freedom. They will argue a lot, which will lead to resentment.