The quick answer is "it's a guess", but a few months ago I looked through each of the fall outdoor leagues that I'm aware of and came up with 102 teams. There are probably other teams that only play indoor or are playing in outdoor leagues not sanctioned by NTSSA or US Club Soccer (YMCA, PSO, etc.)

See this post for number of teams by league.

http://www.txsoccer.info/t4170-02-teams-in-multiple-leagues

Paste this link into your browser, ntxsoccer.org/administrative/clubsandteams.aspx, and you'll see a list of the select clubs associated to NTSSA. If you want a most-accurate count of '02 Boys squads, you'd need to click the link for each club and count the teams in that age group. Most of the links work but not all of them. Most lists are accurate but realize that not all of the clubs are great at maintaining their web data.

If you didn't want to go that leg work, and all you wanted was a guess, I'd say there are about 65-75 teams for this group but they'd come from all over of North Texas. That number would not be limited to just the Dallas area.