Hello, I started practicing a few weeks ago after not touching the piano for over 15 years. Rhythm was always an issue with me. I am retired now. I am wondering if using a metronome will help me or if at my age it might be a waste of time.
IMO: Nothing is a waste of time due to age. The only waste of time is doing something for the wrong reason(s).
If you have trouble keeping a strict rhythm or subdividing the beat properly, a metronome will be helpful.
Working with a metronome may be challenging at first, don't expect it to go easily at first. It will take some practice. Start with slow tempi. Play the pieces with and without metronome. Use it as often as you feel comfortable, it will naturally become easier if you keep using it. The metronome suits pieces from the classical and baroque periods, less so with the romantic era, but doesn't hurt to apply it to these as well as long as you get away from it in your interpretations.
I prefer the metronome smart phone apps, and using headphones.