Age calculator (bootstrap, css, anime.js custom input validation)

second Bootstrap project, I think I'm getting the hang of it, It's really about know what it can and can't do and find the middle ground, however input validation was inconsistent cross browsers i.e maxLength min max input attributes didn't work on firefox, that plus Bootstrap input validation is not accessible so I had to build mine.

I tried building a nice animation but the code was so big and a bit messy, so I went the easy way and used Animejs great animation library see original animation here and the code