Can you built muscle if you are over 50? Well, I’m a living example of that. I gained almost 20 pounds of muscle in a year, starting when I was 52.
Supplements are a topic of high interest, and I did a whole episode on them:

Episode 67 on supplements: https://runningafever.com/raf067-the-real-deal-about-supplements/

With regard to general health, there are some recommendations specifically for people over 50. This information comes from the AARP website.

Vitamin D and calcium – As we get older we are at risk for bone loss. In women, estrogen helps maintain bone mass, so they are especially at risk after menopause. As you probably know from dairy marketing, Vitamin D and Calcium are important for maintaining good bones. Personally, I don’t drink milk because of the lactic acid content and the fat. But Vitamin D and Calcium are readily available in the grocery store. AARP recommends 600IU of Vitamin D, and 1000mg of Calcium (1200 for women) per day, ideally taken in two doses.

Omega-3 fatty acids – These are good fats which reduce inflamation, reduce plaque buildup in arteries, and control blood sugar levels. Taking 1000mg a day can reduce the risk of heart disease, cancer, and Alzheimer’s. I personally take fish oil.
The fish oil supplement I use, smaller pills: https://amzn.to/2LF9Vu2

Probiotics introduce healthy bacteria, which can improve gut health in people over 50, who can be vulnerable to unhealthy bacteria. A healthy gut makes sure you can absorb the nutrients you need. 1-10 billion CFU’s several times per week is recommended.

Not every listener, I know, is working on building more muscle, but you probably should be. Take a look at this condition:
https://en.wikipedia.org/wiki/Sarcopenia

When it comes to building muscle, much of the advice that applies to younger folks applies to people over 50. The problem is that our body’s ability to repair itself declines as we age. The same amount of repair can take twice as long. Which makes it especially important, if you are using supplements, to take them every day, even on rest days.

However, one thing that becomes more important isn’t a dietary supplement at all, it’s sleep! When you are sleeping is when HGH is released, Human Growth Hormone. Testosterone and melatonin are also released during sleep. These are hormones that are important in the process of repairing and building stronger that is the whole reason that weight training works. If you don’t get enough sleep, you will be deficient in these hormones and will need even more time to repair the damage done during training. 7-9 hours is recommended.

Episode 179 devoted to sleep:
https://runningafever.com/raf179-5-reasons-you-need-more-sleep/

References:
https://www.aarp.org/health/drugs-supplements/info-2015/must-have-supplements.html
https://www.fitfatherproject.com/building-muscle-after-50/

Weight 7-day Avg. (change since Jan 2018): 221 (-54)
Workout time: 10 Minutes
Total Distance (total since Nov 2017): 0 Miles (464.04)
Steps: 6,120
Muscle Mass 7-day Avg. (change since Aug 2018): 152.65 (+9)
Body Fat 7-day Avg.: 31%
Daily Sleep Duration 7-day Avg: 7 hours
2019 Goal: 15% Body Fat