My personal plan for insuring my old age is multi pronged.
First, I have secured property that is likely to increase in value. This has been a challenge, but finally it is coming to fruition . I feel property is the best investment that can be made because it is a non reproduceable commodity. Said another way, " they ain't making no more land".
This insures that it will increase in value over time. Also, when you own your own property it is possible to eliminate housing expenses which are a major concern in old age. Especially in cultures that do not look at thier elderly as a priceless resource. In such societies elderly often have to fend for themselves. So to me, this is the most important.
Secondly it is important to have a residual income of some sort. This can be a 401k, or a pension, or at the very least social security that can provide basic needs. Granted, in the US, SSI will not cover basic expenses, but it can be more than adequate for expats living overseas.
Lastly, it should be considered to have a hobby or sideline that can provide some minimal income also. This has two purposes, to give additional income but also to provide activities and purpose in old age. This is what keeps us young and should not be overlooked.