60+Oystercard is valid BEFORE you are 60!

Lisbon

If you live in one of the London boroughs and are approaching your 60th birthday, it is worth applying for your 60+ Oystercard as soon as you are eligible to do so: two weeks before your 60th birthday. Why? Because the card is valid from the time you receive it, which (if you apply online) is usually no more than a week from your application.

The covering letter which comes with the card confirms you can use it immediately (I also gave TFL a ring just to be sure - and yes, you can) - so you could get at least a week's free travel as a slightly early birthday present!

Link: https://www.tfl.gov.uk/fares-and-payments/adult-discounts-and-concessions/60-london-oyster

Middlestitch

Thanks OP - worth knowing, when a week's travel from one of the outer zones to zone 1 could be around £60.