I think your poll is going to look really skewed. If I had to guess I'd say most teens/adults in the world are between 5'6" and 6'... so you are going to get a ton of votes for that and fewer for the outlyers... it's not really going to give good data as to how tall people are, as there is a heck of a difference between 5'6" and 6'.
I don't like the denominations of the poll either. You need more around the average, otherwise you won't get enough distinction and the vast majority of people will fall into one or two categories. I would suggest most of it is okay but around the mean height changing the poll to have groups of just 2 or 3 inches so we can see more variation. For example, around my age the vast majority of males my age or older (or even 1 or 2 years younger) I come across are taller than me, yet I fall into the group containing the majority of people. Either the people I come across are unusually tall or your poll will be missing out on a lot of the variation in height. There latter of these seems more likely.