It's not really all that shocking if his peak years are behind him. There is definitely a precedent.
Sampras never won multiple slams in the same year after the age of 25.
McEnroe won his final slam at the age of 25, I believe.
Wilander won his last slam at 24.
Borg won his last slam at 24 or 25.
And I'm sure there are other examples but these are plenty. The fact is that these were all dominant players and they all had their peak success at or before Roger's age. I know it's shocking based on his last few years, but it can happen.