I started wearing glasses when I was 14-15 years old. I knew because I wasn't able to see the blackboard properly. What I remember the most is how vivid faces started to look on TV after I got my glasses. Until I got them, I didn't realize that I wasn't seeing them as I should.
I started wearing contacts sometime during University but I stopped when I got a car. Being in front of a computer screen all day while wearing contacts never felt comfortable, but when I also had to drive against lights from other cars, it bothered me a lot.
On a side comment, I spent more than two hours trying to wear my contacts the first time I got them. However, when I put on a pair years after the last one, it only took me a minute. Go figure.