My oldest application is about 13 months and I've done two more since then. All were new cars so I simply used a light polish to remove the dealer installed optional swirls from the ground based dirty towels they use. 15% IPA wipe down and straight to the Opti-coat. All three came out perfectly (taking into consideration my level of skill).
I had a few questions after the first application and Dr. G called me back and laid to rest all of my fears (used 1/3 of the syringe on a CRV; that's normal).
I can't recommend this product highly enough. All three live outside in the blazing Arizona sun and they stay amazingly clean. When we wash them, we use Optimum soap but the hose takes most of the dirt before we even get to it. Leaf blower and a 16x16 towel for drips and they look like the day I coated them.