extend the climbout to 600 / 700 ft before turning crosswind
In general it's good practice to climb straight ahead to at least 500 feet before turning. By then you should have the aircraft configured for a best-rate climb (flaps up, trimmed for Vy etc.) so you have time to look around where you're going. And as long as you fly the aircraft you're currently flying (hopefully up to and including your PPL exam) you won't go much wrong with climbing to 600-700 feet and then turning crosswind.
However, later in your career you might encounter aircraft with abysmal climb performance and you might need to initiate your turn well below 500' in order to keep a reasonably tight circuit. Or, if you're lucky, you might be flying aerobatic hotships who are capable of climbing all the way to circuit height well before the end of the runway. In which case you need to fly upwind at circuit height a little before you turn crosswind, otherwise you'll cut everybody off who's doing a normal downwind.
Just something to keep in mind. Turning crosswind should be done at a certain position, maybe a mile or so beyond the runway end, not necessarily at a certain altitude.
Oh, and about not turning below 500': I was lined up in front of a 737. I got my takeoff clearance with "immediate right turn towards XXX". Literally as soon as my wheels left the ground the 737 got its takeoff clearance. My turn to XXX was completed before I got to 50'....