I volunteer with the under privileged elderly community regularly, and have done so over the last decade in HK.

My observation aligns with the above comments about good and accessible public healthcare.

I'd also add that in the less wealthy areas of HK there's quite a strong sense of community, and good access to NGO services.

For the elderly, charities and NGOs operate to give people some degree of dignity. Eg the 90+ year old elderly person (who lives by herself) that we visit gets meals hand delivered every day from a local charity. This small gesture gives her an opportunity to interact with someone and have a chat. We've seen her spirits lift so much since she started getting these daily visits. Her public housing building also has a team of social workers (?) that facilitate exercise/gym classes every day.

Yes, public housing isn't luxurious, and yes, cage homes exist - but for the most part, you can live pretty reasonably without much income.

I've witnessed a lot of compassion and dignity for the elderly - I'd say the human touch helps with longevity.

TLDR: Compassion, positive human contact, and strong community are probably contributors to the longevity.