The answer is 66 because each year, Ben will need as many candles as his age. So when he is two he will have two candles, but they will not work by next year. This means that instead of reusing last year's candles and buying one more, for his third birthday they would have to buy three new ones. It is the same for all the birthdays; when he is four they will buy four candles, when he is five they will buy five more, and so on.
If the candles lasted for more than a year, the answer would be different. If they lasted for all of the eleven years then Ben would only need eleven candles, and keep adding one more on each year.
I have thought of some what if questions for you to solve:
What if on his tenth and eleventh birthdays, Ben only had two candles:
On his tenth he had one in the shape of number one and the other in the shape of zero, and on his eleventh he had both candles in the shape of number one?