Here are things I have done with my DC of the same age.
Day trips: Tubing in Harpers Ferry, hiking Sugarloaf Mtn, Mt Vernon (you could bike the trails nearby), visiting different county parks and doing hiking trails and finding a place to stop for ice cream, finding new recipes and going to a farmers market to get the ingredients, visiting some historical landmarks such as battlefields and taking a ranger tour.
Looking forward to seeing other ideas posted here.