Yes you can wait until next spring to paint the deck. If it is below 50 it is to cold to that type of paint job. It depends on what type of product you use if you can leave the underside bare.
My question is why would you want to paint the deck as sooner or later it will peel and if you just seal it you may have to do that every few years but there is no scraping involved. But maybe you have plenty of time on your hands.

I'd rather not paint it. But the house is white with black trim and I think the deck looks a little funny. Painting it will bring it in line with the rest of the house's aesthetics.

We bought the house last fall and at 122 years old there is always something to do. We've been working on it like crazy. We expect that next spring we will be down to regular maintenance for a couple of years. (we'll spend that biding our time and planning the next remodel).

thanks