What a timely post for me! I just bought my 6 1/2 year old a stroller yesterday (I knew that by the end of the day he'd be climbing all over his little sister trying to fit in her stroller, which she would not appreciate!). When I showed it to him he thought I was nuts, and said that he'd be the only one his age in a stroller! I told him we would bring it and he would only use it if he wants to (which I know he will, particularly when he sees other big kids in theirs).
Because of his size (47lbs and 47 inches), I did not buy a lightweight stroller -- instead, I bought a used full-size Graco at a consignment store and paid $30 instead of $100 new. We tried him in his sister's lightweight stroller and decided it was too hard to push, even though the weight limit on it is 40 lbs. I know that I will be tired when I push it and so I thought I would rather deal with the hassle of a larger and heavier stroller than tire myself out more than necessary. Also, it has a much larger basket (for rain gear, snacks, etc), and I figured that my daughter might nap in it and be more comfy than in her lightweight one.