JAVASCRIPT

javascript today minus 1 day

 var d = new Date();
 d.setDate(d.getDate()-1);

current date minus years javascript

var date = new Date();
date.setDate( date.getDate() - 6 ); //current date - 6 days
date.setFullYear( date.getFullYear() - 1 ); // current date - 1 year

js date minus 18 years

use moment.js