Eighteen.

An alone candle can be blown easily, but... eighteen candles is more difficult. When we are one, or two, even three, is easy to blow out the candles on your birthday's cake, you have lived a short time so you only need a short time to do it. When we grow up, every year you have one more candle on your birthday's cake, every year you have more problems in your life and you have more concerns, you have more problems to solve your problems, you have more problems to blow out your candles.
But.. enjoy the moment because you don't know when is going to be your last birthday, you don't know how many candles you are going to blow out. Thank the congratulations and recive your presents with a smile although you don't like it.

How I use to say, time puts every whore in her corner.
Happy Birthday ;)