Depends, but generally as late as possible.
Many state pension systems allow you to postpone starting to take your pension (some allow you to take it early). In exchange, they will increase the amount you can receive (or decrease it if you opt for early pension). Generally speaking, postponing the pension to maximise your payouts can be an excellent option. Let's look at how it currently works in Japan, the UK, and the US.
For Japan, the normal age to start claiming nenkin is 65. For each month that you delay claiming, your pension will increase by 0.7%. If you delay until 70 (the maximum) you will receive 142% of the usual pension.
Most people that make it to 70 will probably live another 10-30+ years. Particularly as they get older a regular government payment will be much easier to handle than an investment portfolio so it might make sense to spend down your investments if that will allow you to delay starting to take your pension.
The UK system is more generous than the Japanese one for the basic pension, but less generous for postponing. Currently for each nine weeks you postpone taking your pension it will increase by 1%. One important point is that the amount of the base pension will be set when you reach the normal age and will not increase in line with the 'triple lock' if you are living outside the UK or a country that allows for those increases (Japan currently does not).
It seems like you can currently defer social security until you are 70 years old, and your pension will increase by 8% per year deferred. This is broadly in line with Japan.
As a state pension is basically an income floor (insurance against being poor) for many people it makes sense to take it as late as possible, in order to maximise their minimum income. As we talked about in the pensions are not investments post, it is not really helpful to try to figure out how to get the maximum amount out of your pension, but rather to increase your chances of having a comfortable life in retirement.
This means that one useful strategy is to try to save up enough money to live on between retiring from your main job and receiving your state pension as late as possible. This should be possible even for people who are close to retirement if they make an effort or work part-time to make ends meet.
Right now my wife and I will probably take our Japanese and UK pensions as late as possible in order to maximise the amount we receive each month.
What do you think? Are you currently planning to defer your pension? Any flaws in my reasoning?