the pics are not in focus, can't see the fine detail. the tallest ones are long past due for topping.... I prefer to use the "fim" method. Mine are at 5 weeks.. the seeds were planted on March 1st. Check the thread link in my sig.

questions your lighting.. what are you using for lighting, and how much clearance between the tops of the plants and the lights?? Not enough light, and too far above the plants will cause them to stretch and become spindly.