Yes, you can run a report to get all of the youth in a specific date range that you could add to that class. For Example, if you had a class for 14-18 year-olds, you could run a report to show just those children in your database. You would go to Admin-> Reports -> Custom Query. Then choose Date of Birth as the attribute-> is between -> 2004 and 2008-> Run Report. You can then go to Edit Columns and add a column for Family Name, Emergency Contact etc..., to get the info you want to include in that report.
You can then select from that list all the children in that age range, select the down arrow at the top, and add them all to a group (assuming that you have already set up the group in Ministry Areas). I hope this helps.