“Is it wrong to marry someone who is much older/younger?”
The Bible teaches Christians to marry heterosexually and in Christ. These are the issues with which every believer seeking a life partner should be most concerned. Further, sprinkled throughout scripture are clear indications of character qualities that make for happy marriages. A believer is wise to look for such attributes in a prospective spouse.
Beyond that? There are few moral limitations I can think of with respect to a partner, but that doesn’t mean there are no practical considerations.