Generally the question is "Where have you been all these years?" Let's say Mary is asking this question. Mary is referring to years that she has experienced up to now. Mary has missed her friend over this recent period of time so we use the word "these." "Those" would refer to other times that are not recent or that others have not recently experienced. Mary might talk about a school she attended in the past. She would say, "During those years I was at Central Junior High."