By properly taxing companies and rich individuals? Besides, those leaving to 120 would most likely be among the richest of us. Do they really need a pension at all?
Their work amounts to sitting in a hearing non-coherent and voting yes when an aide tells you to. Real people on the other hand spend all day actively doing work for pennies.
By fully funding them. The return from a lifetime annuity bought at 65 is just marginally higher than a reasonable expected safe return from the same investment. (A lifetime annuity pays out on the basis that the provider needs to guarantee an income until you die, so if it returns so much that it eats too much into the capital, it'll be unprofitable for the provider). At the margins, the expected remaining life years of someone at 65 in a developed country is long enough that you can't safely offer that much more without eating away too much at the capital too quickly.