I am trying to add go validation using go validator for dates. I want to compare dates where start date for a model should have a value before the end date .
Your question is not clear, but if you're trying to test a date is before/after another date, take a look at the "time" package from the standard library:
import "time"
var a, b time.Time
/* set dates... */
if a.After(b) { /* do something */ }