Necessary is a relative term. If someone meets the right person at 15 but knows that not staying in touch might preclude a later ability to get back together, then necessary could mean years.
In essence, in communities that do this, “dating” means a best friend. And the person isn’t a best friend because they’re of the opposite gender, they’re best friends because they fit together as friends. And those same qualities that make them best friends could eventually lead to the same qualities that are necessary in a spouse.