Sometimes an old athlete may want to come back for some special match. Some bettors might still bet on him despite of old age and lack of recent experiences in the sport. That is because of what we call nostalgia. They might recall the past memories or past performances of the athlete that may not necessarily reflect the recent performance of the athlete. So be careful when betting because you might just be nostalgic.
The betting results may vary, but with senior players who have an extraordinary history, news will certainly develop and trigger bookmakers to place serious players as favorites with good odds. However, senior players returning to the game are unlikely to be the same as when they were still active athletes. They gain experience, but younger players have the stamina and motivation to prove their great abilities. If there are matches like that, I think what is presented is merely entertainment. It is more commercially oriented to generate profits from the matches, rather than showcasing abilities.