Just to clarify, I applied for a CR1 visa (spousal visa) and my father in law was a joint sponsor. My father in law was 86 years old at the time. I don’t know whether it would change with any other type of visa (I have no experience of other visas!). My husband had zero income at the time so the income requirement was satisfied using my father in laws income alone. I don’t whether it made a difference that I was able to prove I had a substantial amount of savings when I moved and was capable of supporting myself and my husband. The question of the age of my joint sponsor, my father in law was never brought up at my appointment at the embassy. Hope this helps!
I’m not able to find any info stating an upper age limit. What we need is someone who has had experience of having a joint sponsor being rejected for that reason. Anyone?