My Pacific Twin Spots life spans were 9-12 months.
Mine were wild caught, and I lived in a fairly warm area of S. Ca, I am inclined to think more temperate conditions might lead to longer life spans.
Octopus are very interactive, completely different than keeping fish. Tanks were in high traffic areas. I provided a lot of tactile stimulus with different items like hamster balls with crayfish inside, pvc creations and such.
I fed live little neck clams, and other mollusk I acquired at seafood markets.
Octopus are the ultimate escape artist, even the tiniest of holes is an exit point.
Think of it as getting a cat. A responsible hobbyist just doesn't stick one in a tank and walk away, it's an adventure.