A lot of people make mistakes betting on matches like in boxing because of nostalgic reasons yes. One must be reasonable when evaluating a matchup regardless of ones own feelings. If you are not able to bypass this bias I think you should stay away from betting on matches where there is at least 1 party that invokes nostalgia.
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.
You don't have to worry for the athlete in this situation, they are most likely being paid a very generous sum because their historical reputation is drawing in the audience. They will be paid regardless of all the betting that takes place around the event. As someone placing the bet, you should be aware that a previously top athlete is most likely going to bed far behind a top new young competitor. Regardless of what we might wish or hope for - when people get older they lose a lot of the strength they had in younger years and that reflects the outcome of the competition that is being setup. It is mush nore likely the young and upcoming talent is going to defeat the champion from decades ago, so place bets with that in mind.
There are people who are negatively affected by their old favorite losing even if it makes sense for them to lose because of age. Not everything is about money, you can lose some fans this way. I don't want to see my champion that was never defeated finally crushed by someone just because he is old. Who does?