''It's the biggest that's allowed,'' Renfrow said.
The tournament in Rancho Mirage attracted players worldwide. Eight of the 20 in Renfrow's category were from foreign countries, he said.
''The one I beat was from Thailand,'' stated Renfrow.
When Renfrow and his partners, who are in their 70s and 80s, practice four mornings a week at Oberlin College's Philips Gym, spectators will see the men in white shirts and dark pants varying quick aggressive returns with gentle volleys. Renfrow gets to the ball with a pace between a walk and a run, but his aim is precise.
''He plans his shot. He has a good variety of shots. A lot of tennis is strategy,'' said tennis player and friend of 15 years, Kenneth Moore, a retired Oberlin Conservatory bassoon professor.
''He is a marvel. He lives for tennis and he plays rather well,'' Moore said.
Renfrow always wants to go to the courts, in spite of the arthritis that has developed in his hand over the years.
''Certainly my tennis hasn't gotten better. Maybe my attitude has gotten better. I don't care so much whether I win or lose. I'm happy to be playing,'' he said with a smile.
Moore said Renfrow knows much about tennis.
Renfrow and a fellow Kendal at Oberlin resident, Kenneth Roose, advised on the planning of the tennis courts now being constructed at Kendal.
Renfrow explained that ''hard'' courts of cement or asphalt hold up longer and ''soft'' courts of crushed gravel, or what used to be called clay courts, have to be refurbished often.
''I'd rather play on a good soft court, if someone else is maintaining it,'' Renfrow said with a laugh.
He hasn't had any problem finding someone to play, as he has aged, commented Renfrow, and most senior players have played all their lives.
His family had a court while he was growing up in Charlotte, N.C. It was common for families to have a type of court made from an area of the lawn where the grass was scraped away and lined with lime, he said.
''I played my first two years in college, the last two I couldn't even make the team,'' said Renfrow, who earned a bachelor's degree at Furman University in Greenville, S.C. He received his doctorate from Duke University.
He met his wife Toni at the University of Minnesota while she was studying nursing education and he was doing a post-doctoral fellowship. They moved to Los Angeles for their first teaching jobs at Occidental College and began playing tennis together. He became a professor of organic chemistry at Oberlin College in 1944 and had a court at their home.
Organic chemistry, he explained, deals with the organic compounds in protein, fats, carbohydrates and enzymes that make up much of the body.
A shelf at their Kendal home displays a dozen trophies and numerous plaques from their doubles, mixed doubles and single matches.
He reaches for his wife's hand while they sit on the couch. She stopped playing tennis four years ago and is an Alzheimer patient.
''I can play because Toni can go to the Kendal care center. If it weren't for that I wouldn't be able to play. She gets along very well there,'' he said. The Renfrows have a son who lives in Huron County.
The Renfrows enjoyed watching tennis on television and he doesn't mind offering his opinion about today's tennis players.
''Andy Roddick is the best tennis player the U.S. has. I admire the Williams sisters (Serena and Venus), although they've gotten so that they can't beat the Belgians,'' he said.
He also plays croquet, table tennis and bocce.
''If they (senior citizens) like to play tennis, I'd encourage them to keep playing. There are some people who begin in their 60s or 70s, and they do all right,'' said Renfrow. He added he has played in tournaments with some of the same people for 30 years, and whether they are from Germany, Austria or Spain, they are like old friends.