Welcome to EF!
just for the record, I'm 43 and acne is still very much an issue for me when I cycle.
You didn't mention anything about your exercise regimine or training history. Help us understand why you would know like to run a test/deca cycle? You're certainly old enough to make your own decisions but we can be of more help the more we know.
At 47 it's very possible that your testosterone levels have reduced to the point where you have a harder time building and maintaining muscle. If that's the case, a cycle of test/deca will only help you while you're on it. If your natural test is low, then all the muscle you gain will drop back off a few weeks after the cycle. I know because I was in that circumstance.
If you want to cycle, you should get a "before" blood test anyway so why not visit your doctor for a checkup and get some blood work done. If you qualify for testosterone replacement therapy, that will be much more helpful to you than a cycle of test/deca.