I'm convinced that 3/4 of riding is mental. Yes, you need to be in shape... but from what you've said, you still are! I'd go for it. It's not a race, so really who cares how long it takes? (at least that's what I say every ride! )

Get in as much distance as you can and enjoy your ride whatever one you do... and if you ride the metric don't be "resigned" about it... heck 62 miles is a loooooong way... still an impressive ride.