If you need an email address to join yahoo, how can I teach my nephew the internet while visiting for summer?

My nephew is almost 55 yrs. old but is tech. lacking. I want to teach him. He has no email address but yahoo insists he must in order to join. I do not want him on mine. He tried to set one up today and they gave him the runaround. They insist he has to have an email a/c. If he wants one of his own, why does he need a back up. Should he have to join some other svc. first. This is stupid. Kids of school age join all of the time without this problem. I do not want him in my mail as I shop and pay bills and even though I trust him I also have personal things on there. This is crazy since I see kids at the library all the time and they changed theirs constantly, Is it because he is old. One is never too old to learn. Thank you and by the way he does not want his name as his user name. Why all the big deal. I had 2 accounts with yahoo and they messed my second one up so badly that I lost almost all of it on it. There are only bits and pieces left and over 400 drafts. This makes sense?