You have a magic pill, which de-ages you by 20 years. You can take it once in your life only, so long as you are at least 20. What age — past, current or future — do you reckon is best to take it?

I thought like you until I realised medicine is for the rich. Even in countries with universal healthcare there's rationing of advanced therapies.

• Years 10-20 - Human drug trials
• Years 20-30 - Rich people use it.
• Years 30-40 - Appears in universal healthcare systems.
• Years 40+ - Appears in the UK NHS.

There's a few promising senesance drugs in trials but that means you and I won't see it until 2060 at the earliest.