Licensed General Contractor, Painting Contractor, Christmas Light Installer
Water beading is a proven test which is fairly accurate. Anything else would be highly subjective and situational. I would also do a test for moisture content, but that's just so I know the wood itself is ready, not necessarily related to whether or not the current stain has weathered sufficiently. That wood looks pretty dry from the picture I looked at. My guess is the shiny-ness you're seeing is due to the (semi) film-forming properties of ProLuxe. I don't think it'd look any less shiny if you waited another year honestly, unless you strip it.