Can a person build muscle at the age of 50?

yes, if you are still willing to exercise

Some considerations though. After the age of 30, your level of both testosterone and growth hormone will begin to decrease, What that means for muscle growth is that your ability to recover will also decrease. You will need to become more efficient in the exercises you choose (mainly compound exercises) and the time you spend working out. Don't work out more than 3 days per week. It will take longer to recover. Do some cardio exercise as well; roughly 3 times per week. Most important: pay attention to your diet. Balanced, with sufficient levels of protein, low fat, and moderate carbs. Eat as healthy as you can. Make sure you get enough sleep. This varies, but at least 7 to 8 hours per night. You wont make as good progress as a 20 year old who is going all out, but if you go all out, you will be stronger and in better shape than most guys you see on the street.