Also DC Stoddert (
www.stoddert.com) rec league for NW DC. At age 8 even though some kids may already be moving toward travel, suspect in his school grade that there are one or more rec teams, and playing with his friends probably would be more attractive than signing up for a rec league and being placed on a random team that needs players (often can be a bad sign if a team can 't fill with kids from one school or neighborhood, ie the parent coach is a nutcase or no organization or something).
And if he is really interested, and doesn't want to be way behind in terms of having no idea about the rules or how to kick a ball or dribble at least a bit, he could do a one week soccer camp this summer, there are plenty around held at various parks and private schools. If he is already athletic and big, just a few days of a soccer camps or a few clinics will catch him up instantly. For instance Bethesda Soccer Club runs weekly camps all summer at Sidwell Friends lower school campus in Bethesda, link is
http://premium.bluesombrero.com/bethesdasoccer/Home/CampsandClinics/tabid/14167/Default.aspx