Stranger/Separation Anxiety

I had it in my head that if Seth were to have Stranger or Separation anxiety then he would have already had it, well yesterday I read that it actually peaks around 18 months. I think Seth may be entering this stage! He has become a lot more clingy to me especially around new people or people he hasn't seen in a while. Yesterday when my mother in law arrived from Atlanta (Seth's Nona), he acted more shy than usual and kept coming over to me and holding on to my leg or wanting me to hold him. The good thing is he really just acts shy and doesn't freak out and he also warms up to people very fast!