What is a regular weight for a seven month rottweiler...

That's about right but of course it all depends on his overall stature. If his torso is neither too roly poly nor too skinny, don't worry.
I've seen large dogs who seemed to reach what looked like full size by that age, but then changed shape a little more at about a year and then again around 18 months, without really gaining or losing weight. A lot depends on exercise and diet too.