I'm 288 months old

Why do people refer to their kids in months? I mean I understand when they are little like 6 months or anything before a year...and I even kinda understand months all the way up until two. Because until that point most kids clothings are in months....but past that they are YEARS old not months. I saw a woman today with her adorable kid in her sig....and underneath it said 38 months. Are you fucking kidding me? I had to use my caculator to figure out how old he was (not really...but ya get the point)