I understand that you can withdraw above the minimum sum once you hit the retirement age. However what if the retirement age is increased to say 85 in 30 years time?

That is abit extreme.. Dun think Govt will do that due to possible backlash from citizens.. At most is give lesser to extend the payout longer.. No point worrying about this in 30 years times..

Logically, any changes in the retirement age have to be supported by the statistics on the longevity of Singaporeans. So unless Singaporeans are statistically living past age 100 and above, I would not be too worried about the low probability of increment in the retirement age to 85.