"I think it is a woman, and she could be older," Mayweather said after beaten the Mexican by majority points decision in Las Vegas on Saturday night.
The judge, CJ Ross, surprised many by giving six rounds to Alvarez. She was also one of the two judges who scored in favour of Timothy Bradley over Manny Pacquiao last year; another controversial decision.
Mayweather also said he had dislocated his left elbow in the middle of the bout over previously unbeaten Alvarez.
The 36-year-old Mayweather earned a record $41 million purse for a dominating 12-round victory in which he claimed Alvarez's WBC and WBA super-welterweight titles.
"I could have used more combinations down the stretch. I think I dislocated my elbow," said Mayweather at the post-fight news conference.
He said he was unable to use his jab in the sixth and seventh round because of the troublesome elbow, although round seven turned out to be one of his strongest of the fight.
"My arm was hurting, and I wanted to stop using my jab and just paw with it," Mayweather said. Doctors will examine the elbow this week.
He used his superior hand speed to keep Alvarez at bay, but Mayweather still only managed to win the fight on two of the three scorecards.
Ross scored it a draw, 114-114. Craig Metcalfe (117-111) and Dave Moretti (116-112) had Mayweather winning.
The American gave away 13 years in age and almost 7 kg in weight to the younger and stronger Alvarez.
The Mexican weighed in right on the 69kg catch weight. But by the time he entered the ring, he 75 kg – 4.5 kg heavier than the weight he had been sparring at in the week leading up to the fight.
The added weight made him look slow and awkward in the ring as he suffered the first defeat.
Mayweather plans to fight twice in each of the next two years; in May and September. He said several times after the fight he was counting down the months until retirement. He believes he will stop boxing some time in 2015. "I only got 24 months left," he said.