I looked at some pictures of the ride (40 miles isn’t it?). It looks like people are riding everything from mountainbikes to hybrids to road bikes, so my spontaneous reaction would be that you’ll be fine on your Kona Dew.

Obviously, the more miles you can get in before the ride, the more your body will be in shape for it.
My rule of thumb is that if you can ride half the distance fairly regularly (say once a week), then you’ll be good for the whole distance without too much stiffness the day after.

As you said, you’re 39 in good cardiovascular shape. I’d go as far to say that if you haven’t even ridden a bike for years - and start off gently and keep to an easy pace - you’ll be good on the day. Have fun!