Patent US3516422 likely expired in 1987. Anyone can practice exactly what is disclosed in that patent. However, there is no guarantee there aren't other more recent patents that also may relate to a product. As you found there is a patent application US20160206031. This is an application, not yet a patent. It may or may not ever become a patent and even if it does, the claims may be changed or narrowed from what is in the application. In this case US3516422 is considered prior art to US20160206031. There is very likely to be other prior art too.
From what I can see, US20160206031 is different from US3516422. In the case of the US3516422 there is a substrate glued to the eyelid to which a magnetic false eyelash is the attached through magnetic attraction. With US20160206031 there are two separate magnetic false eyelashes placed on either side of the users natural eyelash. The magnetic force keeps the two magnetic lashes clamped to the natural lash.
I deduced from your comments from your closed question that you had a similar product and received a request to stop selling your product from the owners of US20160206031. You should consult with a patent attorney as first, US20160206031 is not an issued patent and may never become one and second it is possible that your product doesn't actually infringe on that application. A patent attorney is best able to provide guidance.
With regards to your second question, the application was filed on July 16th, 2015 and has a priority date of January 19th, 2015 so any publication after that (and I believe up to a year before) won't invalidate the patentability. If you can find a publication before January 19th of 2015 it may be grounds for invalidation.
Please understand that I am not an attorney, so please don't construe my answer as legal advice. Definitely consult with a patent attorney for that.