Target $1m share portfolio at age 65 returning 4% p.a., so you get $40,000 dividends a year.
This is possible due to compounding - use a compounding calculator, $1,000 a month for 35 years at 5% should hit the $1m mark.
35 years meaning from age 30-65 - people usually start work in their 20s, but don't have enough salary to invest in their 20s so I am conservative - if you are able to start in your 20s, even better, the $1m target is more achievable.
But in your 30s, you should hopefully have gotten your first job promotion, a bit more salary, able to set aside $1k a month for investment).
If your flat is fully paid up, and you have hospitalisation insurance and basic eldershield, this should be enough. Furthermore, you can pass on your shares to your children unlike other plans which stop when you die.