When did you start forgetting?

Im only 21 and the other day at the drs they asked me my age and I was just about say 20 when I was like 21?..... yea im 21? Its kinda bad but ya look forwad and count down 16,18,21 and after ya dont have any big milestone ages that have good advantages tide to em. maybe older ages to get aarp discounts or the age to retire but thats about it.