Yes, it’s actually very good for exercise and health/happiness. They would be safer if they don’t paddle alone though, but this is also true for everyone. A heart attack or any other health issues that can come with age should be considered on an individual basis. Paddling back during a heart attack or waiting for coast guard response times might not be favorable circumstances. Your Dr. can tell you if it’s something to avoid and heart monitoring watches can be worn. I’m 50 , paddle alone about 1/2 the time, have regular physicals and it’s my go to exercise. Being old doesn’t mean you stop living but eventually eye sight, hearing and other age related issues might need to be considered to stay safe in the water. Dehydration and heat exhaustion might come faster on a hot day but unlike a golf course you can cool off in the water. Staying close to shore and in cell phone coverage w a life jacket on can make a big difference in an emergency for anyone at any age.