Better stamina than Ronaldo? I would bet if they had to pass a fitness test that most of the time Ronaldo would be the one who comes out on top. I think even the toughest haters of Ronaldo have to admit that his physical condition is insane for a guy at the age of 38. His stamina is not to be confused with his top speed although I think that he would still be faster than Mane as well.
It is unfair to compare stamina, fitness of a player who is 38 years old and another player who is only 31 years old. We know after 30 years old, athletics can have big differences, changes in their stamina, fitness and strength. And here we are talking about a difference of 7 years that is not small.
Many players even don't continue to play at their 35 years old and very few players who can play till their 38 years old. Here again I think we should repeat Cristiano Ronaldo is still playing and his performance is very good. Many young players even can not play as same as Cristiano in this season. Mane is strong but I am not sure he will still playing at his 38 years old.
But his stamina is probably better than 90% of the players in the Saudi Professional League at least. But one issue for him could be the motivation and the last few percentage points in terms of performance. He is used to play against the best teams in the world in front of the best fans in the world. It could lead to a lack of motivation when he doesn't play on that level anymore.
It is true that he is super professional and his body is very strong and sustained well over many years. It can be gift for him because he was born with a good body but I believe his professional lifestyle and training help him a lot to gain such amazing body strength. Without professional, he can not prolong his career till 38 years old.
Without a doubt is his lifestyle the key to his physical condition. Again, if people complain about his character or attitude or whatever they can come up with, his determination and dedication to preserve his best physical condition is unbelievable. In that regard he is a role model for literally every human being around the world although we should not forget that he has access to supplies and expertise that rarely anybody else has outside of professional sports. But still it needs a lot of endurance and also passion to live a healthy lifestyle like that from early in the morning to late in the evening for decades.