Belgian Tervurens typically stop growing in height by around 12 to 18 months, but they may continue to fill out and gain muscle mass until they’re about two years old. Like many medium to large breeds, their growth rate slows down after the first year, with most of their height being reached in that time. After they’ve reached their full size, it’s usually a good idea to switch them over to adult dog food to support their maintenance needs rather than rapid growth.