Honestly, the right time is different for everyone, but a few things usually come up.
Most people start considering body Contouring after losing a good amount of weight and being left with loose skin or stubborn areas that just won't shift. Same goes for after pregnancy, some areas don't bounce back no matter how consistent you are with diet or exercise.
Age plays a part too, skin naturally loses elasticity over time, and fat can settle in new places.
Really it comes down to noticing an area that bothers you and hasn't responded to anything else you've tried. If that's where you're at, worth getting a proper consultation to see what actually makes sense.