My aim is to accumulate 21 bitcoin so that no more than 1 million people can have more bitcoin than I. If bitcoin is widely used then, I can retire comfortably.
although 21 bitcoins may be not enough but you have a great targer there! goodluck 
Yeah that is a nice start to get bitcoins, always have a target what you want with bitcoin.
Me personally I want as minimal 50BTC in the future.
I think it also depends on how much money you need to live in your retirement stage. If you need a lot of money then you're going to need more.
Also depends on what country you live in, incase bitcoin doesn't adapt as we all wish for it to be.
For some country 100BTC is more than enough, because is so cheap there.
Where I live now everything is just expensive, so I am just planning when I am old I just retire in a country that I can live with just 100BTC.
If I may ask where do you live? How good is the daily routine in your country like work?
Because when I am 40 maybe I can retire there. But I think you live in asia right?
vietnam to be exact if you live comfortably enough, and the price of bitcoin when you retire is 1000-2000 which is likely to happen then it's enough I think 
