As I've grown older and more secure about what I am I've done it less and less during that transition into being an adult. I am still in contact with somebody I met online when I was about 12 or 13 and I eventually had to go back and talk about everything i'd said just for my own peace of mind to explain why I was insecure enough to be dishonest about this or that fact, since young boys have a special kind of stupid sometimes.
I lied about having my first girlfriend because I was afraid of being 'late to the party' so to speak, and hated so many things about myself that at the time I felt like i'd never have a relationship despite only just reaching the point where hormones were coming in to the equation. I lied about my weight at the time during puberty when I was heaviest, I lied about my age to people to be accepted, I lied about all sorts of things and none of them make me proud (as you can see, most of them are typical teenager nonsense worries about girls, appearance and achievements and proficiency at this or that subject or part of my life).
It's one of those things you look back on and face palm a little, internet being what it is it doesn't tend to hurt anybody when you move between communities every so often and the ones you do stick with don't remember most of it and are sympathetic because they watched you progress over time.
I probably still unconsciously stretch the truth about things which make me insecure. There's also that same compulsive urge to want to seem more intelligent than I am, that everybody has.