What are some good investments for the elderly, considering they may not have a long investing runway?

What you should be looking for are guaranteed, fixed income products.

Short term high quality bonds, annuities, money market instruments, and social security.

Your focus should be creating streams of guaranteed income with an emphasis in wealth preservation.

It is always never too late to start investing. The only potential drawback for elderly is the short investment timeframe and the risk level.

Elderly should not expose themselves to unnecessary risk. The last thing we all want is to lose money meant for retirement. Therefore the safest bet would be with the Singapore Savings Bonds. It is capital guaranteed by our government and pays a reasonable interest rates.

Government bond or corporate bond can be one of the options.
I'm slowly increasing my bond allocation every year and expect to have 50% bond in my portfolio when I retire. Just for yr reference.

The rule of thumb is definitely choosing a less risky option.
However, it is also not wrong to study stocks and choose your own sticks. Due diligence will reduce your risk.
Look at how old Warren buffet is. He still continue to update himself and invest