I used to be fine with heights when I was younger. I think it all changed when I hit my mid 20's and now I can't be fucked with it at all.
I've got photos from a school trip to Paris where I leaned over the safety rail at the top of the Eiffel Tower to get a better picture angle, straight down. I was balancing on my belly, feet off the ground. Not a chance I'd go near the edge now. Probably wouldn't even go up in the first place.
Last October I shit myself on the Liverpool eye every time it got above the roof of the Echo. Every gust of wind made me shake like a leaf. The missus was highly amused.