Based on this list of turtles in Massachusetts, and this one as well as the pointed nose and the jagged back shell, I am going to say that this is a common snapping turtle.
For more information I would suggest Wikipedia.
It a good thing that you husband didn't touch it, because they are capable of biting (link has gross picture).
This is a common snapping turtle. It's not a tortoise. The biggest difference is that turtles are aquatic, spending most of their time in the water, while tortoises live on land.
As for your other questions:
It's not easy to tell the age of the snapper. They reach full size between 8 and 10 years old. Adults measure from 9.5 to 14.5 inches (24 to 36 ...
This does look like some sort of turtle. Snapping turtles can easily get to the size you mention, and are fairly common. The picture doesn't give the impression the tracks are really 10 inches apart. They seem narrower than that, which would open the possibility for a number of other turtles. Box turtles get to a reasonable size, and then there are a ...