While the intensity between the two is fresh and still getting the attention of the fans, they will consider it but if not, it's fine then Floyd has proven himself already and he's happy to have that win against Manny.
In short, if Floyd Mayweather Jr. will not accept the challenge of Manny Pacman Pacquiao for the rematch, it is really mean that Floyd Mayweather Jr. is playing safe, he maybe doesn't want anymore to get a lose by Manny Pacman Pacquiao and want his record clean with 0 loss.
Even if we based on their age which Floyd Mayweather Jr. is current on his 42 years old, and Manny Pacman Pacquiao is 40 years old, they can still fight since the gap is not too much, another big fight of the year once this will happen.
The age isn't the problem, they are making the interest of the people as a sole business. We as fans, we really want to see this fight and no doubt that many would love to watch the fight and get the tickets even with pay per view.
And I don't want to expect that this match will actually happen, Floyd might already have the sense and standing with his words that he literally retired and wanted to settle his career without a loss.