Frankly, there is a huge difference between 12 and 18.
That depends on the intention of the poll, and I'm sure it wasn't to offend anyone. For example, when it comes to disposable income, the difference is very small. In fact, for most intents and purposes I can think of for a poll, the difference is small.
If the intention is to find out why so many forum posters act like disgruntled twelve year olds, then I'd agree the difference is big.