Extremely realistic. In fact, a growing number of volunteer schemes are removing the upper age limits (though they maintain the lower age limits of 18 or 21).
As long as you’re healthy – and yes, that does seem to be a requirement in most if not all cases – finding volunteer work in your 60s, 70s and beyond is becoming easier every day.
Senior volunteers as a group have different needs and aspirations than 20-year-olds, so if you’re an aspiring volunteer, you should keep these in mind when you search for your placement.