Can the defense rush the quarterback in 10U?

Yes. In 10U the standard NFL FLAG rushing rules apply (rushing is only banned in regular-season 8U and younger):

• Up to two players may rush the quarterback.
• Rushers must start at least 7 yards from the line of scrimmage at the snap, behind a rush line marked by the official.
• Rushers must raise a hand before the snap and must rush immediately; a delayed rush isn't allowed.
• Once the ball is handed off, pitched or lateraled behind the line, any defender may cross the line of scrimmage.
• Rushers may try to block a pass, but contact with the quarterback (unless incidental) is roughing the passer.

The quarterback has a 7-second pass clock. If they don't throw in time, the play is dead and the down counts. Defenses are never required to rush.