I do not believe that every Christian should adopt. (I do however, believe that every Christian needs to be doing s.o.m.e.t.h.i.n.g. about the orphan crisis.) But IF God should call you to adoption . . . or foster care or global orphan care or whatever . . . are you WILLING to say "yes, Lord?"
For me, willingness is often the true issue when it comes to matters of obedience. In the case of adoption, issues like parental age, size of house, size of income, ability to get off work to travel, medical history, number and needs of other children in the house, etc., etc., may truly be legitimate issues--but in other cases some of these may only be excuses. God knows the difference--and I think deep down in my heart, I know the difference, too.
Sometimes--often, actually--the foundational issue for me is that I just plain don't WANT to do whatever it is that God is speaking to me about. And in the end, I finally have to come to grips with my will. If Jesus is truly LORD of my life--well, doesn't that mean that He is the boss? That His word is my command? No will but His will?
God may call you to adopt or He may not. Are you WILLING to obey?