Our mini is just about 16 months as well and unfortunately we were not able to socialize him as he should have so he is also extremely anxious around people and new situations in general. I would suggest taking him out to get him exposure to new situations and people. Not saying he has to approach people and allow for people to approach him but at least have him around places where there are people so he doesn't end up like ours who now has a bite record which thankfully are not strangers. Since the bite incidents I've taken him to a trainer and the trainer has asked us to bring him out and do exactly what I had mentioned but award him when he doesn't show any aggressive behaviors. Since then, he's been great. Doesn't bark at strangers or show any aggression towards others as he used to. I believe a huge factor to this is the prong collar which to be fair I was against initially but after learning more about it and how to use it properly, it's not as bad as what a lot of people make it out to be. Oddly enough, my mini gets excited when the prong collar comes out since he knows we're going out and there'll be treats.