Labrador Retrievers generally stop growing in height by around 12 months of age. However, they tend to continue filling out, gaining muscle mass, and increasing in weight for several months beyond that. Most Labs reach about 85% to 90% of their adult size by 18 months, and full maturity, including filling out the bone structure and muscle, can be reached anywhere between 18 months to 2 years. In some cases, they may continue to fill out and mature slightly up to 3 years old. Key points on Labrador growth:

• Rapid growth occurs in the first few months, with the most rapid weight gain between 12 to 14 weeks.
• By 6 months, they typically reach around 75% of their adult size.
• Height is usually near final by 9 to 12 months.
• Full adult weight and body filling out happens mostly by 18 months to 2 years.
• Some larger or slower-developing Labs may take up to 2 to 3 years to fully mature.

In summary, Labs stop growing taller mostly by their first birthday, but continue to gain weight and fill out until about 18 months to 2 years old, with some variation depending on the individual dog's genetics and nutrition.