We just finished power washing a deck that is almost 2 years old but has never been stained or sealed. Our intent was to use Sherwin Williams Clear Deck Sealer. A local "expert" has suggested that the power wash took the deck "back to green" ... that is, nearly new. Can that deck sealer be used on this possibly re-greened cedar deck ... or how well will it work and hold up. Second question, the "expert" said not to apply this is hot sunny weather as it would then peal off in one year's time. Is that correct? Thanks in advance.

You should be okay with the power washing.

I would look into a better stain then the SW. It is not a very good product as it is prone to peeling after a season and is hard to remove when you decide to switch to a better brand.