2cm Shorter

OMFG !! When I was in secondary school, my height was like 173cm (without shoes). Then today, I went to weigh myself, I was 173.5cm. (with shoes). I thought I was growing taller which was good. Then my friend asked me to take off my shoe. WAA !!! Become 171cm !!! WTF !! Is it true that when people is growing older, our height will slowly decrease??