First I would suggest not to get confused or tensed, there is nothing to worry. With your query posted here would get many thoughts, here are my 2 cents.
If we compare's dog's age and corelate to human's age - 1 dog year = 7 human years. If we look at your dog in terms of human years, he has just turned 16, do you think a 16 year human is old enough to reproduce, I am sure he is not, that helps answer your question on the age and ability to reproduce.
Coming back to playing situation, are you sure the female dog was in heat ? and how many days she was she in when the female's owner came to your house ? which in your query has not been mentioned. Help post that piece in the qerry.