Do you think it's possible to have a good age disparate relationship, like 20 years difference?
It's very possible I know because I am in a relationship with 21 years. It really doesn't matter how old you are as long as you love her and she loves you. But she has to be able to accept the situation you are living in. Stability isn't needed for most but some will need it.
older or younger?
eh? One of them is going to be older or younger..
I think the hard thing is, the older person is going to die on you too fast.
Such relationships are possible (and not as uncommon as people may think), and may very well be fruitful; but yes, >>4 is right, the older one will leave the younger one. Both need to be aware of the fact that death will do them apart. This works as long as the younger half is mature enough to handle that decision. The younger will always be left, and that person will undoubtly need to make a decision sooner or later to stay widowed or look for a partner once more, in his/her midaged life. Their significant one will not last forever.
Give us the ages. No good saying it's all right if for example, one's 13 and the other's 33. Know what I mean?