We received the same photo and question yesterday from a person that selected Baltimore County as their location, but will paste our reply here in case someone you saw the plant with happened to submit the same query:
The foliage shape and leaf arrangement looks like lilac, though we can't be certain (it's hard to see enough detail, and flowers are key to confirming plant ID), and several species of lilac can be grown in Maryland, though we rarely see them produce seedlings. If you're able to take a close-up photo of the foliage, we'll see if any other species come to mind. Otherwise, we might not be able to get more specific until it blooms, though that might require another year or two (at least) of maturing on the plant's part.
Thank you for your response. The other inquiry may have been mine too. I live in Baltimore county, but this plant is in my son's yard in Howard county. Here is a close up of a leaf.
