A lobster’s age is approximately his weight multiplied by 4, plus 3 years. A lobster is approximately 7 years old before it is legal to harvest, and it will weigh about 1 pound. A 25 pound lobster could be over 100 years old! A lobster may live 100 years, grow to 5 feet, and weigh as much as 45 pounds! Officially, the largest lobster ever caught weighed 44 pounds.