Your 90 year old grandfather can teach you more than you think just by talking to you if that is "doable"
You are a young pup. talk to him, ask alot of questions. They love it and it is good for him. write it all down. you won't regret it.
Later , when you are working with another's help, a thing or two your Grandfather said might make all the difference in the world with the way you do something.