For FIRE, what is the earliest retirement age for Sgreans? How much capital minimally do we need to retire early in SG? (On average for both)

I think the sooner you reach $1 million buck, the sooner you can afford to FIRE. Of course whether you decide to get married and have kids will play a part too

Depends on the lifestyle you want. I know of people who can survive with under 1k a month or need 3k a month. Of course, the lesser you need, the earlier you can start?

Retirement for everyone is defined differently. Does retirement mean you get to do what you like with your time? Or isit to stop working?

Depends and depends