At the risk of sounding crass, will the guardian be changing the child’s diapers or will the child be changing the guardian’s diapers? If the latter, the guardian is too old. Having a guardian who is too old makes things difficult for both the guardian and the child. A senior citizen cannot easily take a child to basketball tournaments, help with algebra homework, and enforce curfews. Sure, there are some seniors who would easily be able to handle all of the above, but those are likely a small minority. Practically speaking, if you place a child in the care of a senior citizen, the child will end up being the caregiver of the supposed guardian. You don’t want to put your children through that.

At the lower age range, the guardian must be at least 18. I would rarely recommend placing young children in the care of an 18 year old. However, a 16 year old sibling may in some cases be placed in the care of his older brother or sister.