13 - Number of years since the Capitals had two teenagers (based on age on February 1 of that season) in the lineup on Opening Night, as they did on October 6, 2000 when they dressed 19-year-old Kris Beech and 18-year-old Jakub Cutta against the Kings. Of note, Beech would play three more games with the Caps before being returned to his junior team in Calgary of the WHL, and Cutta would play two more for D.C. before being sent back to Swift Current of the same league.
Since then, the Caps have only had four teenagers (by the conventional definition) in their opening night lineups - Brian Sutherby in 2001 (at 19 years old), Steve Eminger in 2002 and 2003 (at 18 and 19), Boyd Gordon in 2003, and Nicklas Backstrom in 2007 (at 19). That could all change tomorrow night in Chicago, of course, as a pair of 19-year-olds - Tom Wilson and Connor Carrick (both of whom will still be 19 on February 1) - could get sweaters for the season opener.
[Note: Edited for accuracy after the fact... it's still preseason for everyone...]