Your father is right, redwood does not hold paint well. Over the years, I have had to contend with peeling on redwood siding more than with any other type of siding.

I never like full bodied paint on any deck built with traditional joist and spaced decking lumber. There are too many ways that moisture can enter the wood, i.e. thousands of nails/screw holes, joints, decking sitting on un-protected joists, etc. Once the moisture is in the wood, the paint film prevents it from getting out and peeling results.

Redwood is inherently rot resistant. If you do nothing but keep the mildew and fungus under control with periodic cleaning, it will last just as long as if your faithfully coated the deck with stains or paint!

If you want to keep the natural look without the graying, you only need to give your deck a periodic cleaning with an oxalic acid solution. Several manufacturers have such cleaning solutions, Behr and Cabots, etc. The acid solution is actually quite mild. It will get rid of any graying. Personally, I would consider a periodic light coat of clear decking oil, such as Cabot's "Clear Solution". This will give your redwood a little luster and help slow down the drying of the wood and splitting which results. Clear Solution also comes in several tints, but the clear version will not have a build up of color.

Unfortunately, you will have to remove that solid paint film first, either through sanding or chemicals. Not fun,but doable.