Seeing as ANH Obi-Wan has done nothing for a good twenty (give or take) years, that sounds fine regarding swordsmanship. Dooku was far older, but, then again, he was never out of practice for two decades. Same with physical fitness. While the Force can grant a strength above the normal man, Obi-Wan's strength had obviously decreased with age due to inactivity.
Can't use Yoda or Dooku or Palpatine as good examples for that, because they didn't go for power-blows really ever.
Luke was a Jedi Knight by the end of ROTJ (albeit a half-trained one), so he could at least stand his ground against the Sith Apprentice (albeit a highly deadly one).
In the Visionaries comics, Maul hunts Obi-Wan to Tatooine a year or two after Ben delivers Luke to the Lars homestead. Obi-Wan manages to subdue Maul, but doesn't deliver the killing blow (which would have been to ignite his lightsaber through Maul's forehead), instead leaving Owen Lars to put a hole in Maul's head with a blaster rifle.
Then again, not really canon in an EU sense.