How old is too old to build muscle and gain strength? The short answer: When you’re dead. AI Image First and foremost, there are zero qualified research studies that show an age when muscle, strength, and endurance cannot be developed. You can be 50, 70, 90, or 100. If you strength train, beginner or long-time exerciser, you can build strength, endurance, and even mass. These may take more time and be harder to do as we age, especially building muscle size. But the most common goals…