I would use the noun form instead and use "Single Elder Household" or just "Single Elder" since the context of the heading may make it clear that each is a type of household. The word "elder" can be used in this type of context to mean "elderly person."
Elderly or elder is too vague unless it has been defined elsewhere. I much prefer 65+/70+. 'Elder household' sounds very odd to me. I suppose there are other categories so you don't repeat household each time.