I am surprised this subject has not been discussed here.

My son was 16 in September. A few days before his birthday, we applied
for a child Oyster card at our local Post Office. The first clerk
thought the application was invalid but was overruled by his colleague.
The application then went for central processing.

This week, a card valid until October 2006 arrived.
By then, the age limit should be 18.

It seems that any valid application made before the 16th birthday will
result in a card with a year's validity.

My local post office has application forms but no leaflets.
--
Walter Briscoe