Separation anxiety can start at a variety of ages.  Most experience it closer to 9 months, but some experience it earlier and others later. We do prefer approaches that are connection based, but separation anxiety can be exacerbated in children when parents come and go or linger too long during the separation period.  Here are some helpful blogs discussing approaches to dealing with separation anxiety:

Soothing Separation Anxiety

Conquering Separation Anxiety

Handling Separation Anxiety

Playful Ways to Heal Separation Anxiety