What age did your puppy start to grow slower?

Hello, looking for advice.

What age did your puppy start to grow more slowly? I've been weighing mine every week, just to monitor that he is growing healthily. My Tibetan terrier puppy is 18 weeks (4.5 months) old, and the last two weeks he's gained around half the weight he normally does. 200g this week, compared to around 400-500g previously. I've seen that puppies only stop growing when they're around 6 months. Am I being overly worried?