Not buying it. Different sport requiring a much different skill set, particularly at the edge positions like CB and WR. What makes guys like DeSean Jackson and Steve Smith special is their elite speed/burst. If they lost a step, they would no longer have elite speed and there would no longer be anything special to distinguish them from the legions of mediocre talents (see: L. Tomlinson).
Out of curiousity (because I really don't know which set of WRs would age more gracefully), I fired up the Historical Data Dominator and got a list of every WR who ever posted a 1000 yard season at age 34 or older. That produced the following list of 22 names:Jerry Rice - 6'2"Joey Galloway - 5'11" Jimmy Smith - 6'1"Tim Brown - 6'0"Cris Carter - 6'3"Henry Ellard - 5'11"Irving Fryar - 6'0"Drew Hill - 5'9"James Lofton - 6'3"Derrick Mason - 5'10"Terrell Owens - 6'3"Rod Smith - 6'0"Tim Brown - 6'0"Isaac Bruce - 6'0"Donald Driver - 6'0"Bobby Engram - 5'10"Marvin Harrison - 6'0"Charlie Joiner - 5'11"Frank Lewis - 6'1"Tony Martin - 6'0"Art Monk - 6'3"Pete Retzlaff - 6'1"First thing that pops out at me? Only 5 of the 22 guys were 6'2" or taller. Also, of the 22 guys, I'd say that 19 of them were guys who, stereotypically, were more likely to get yards than TDs (the three exceptions: Rice, Owens, and Carter, all 6'2" or taller).Now, obviously just because a guy is 6' or shorter doesn't mean his game is based on speed and acceleration (Bobby Engram, anyone?)... but, with that said, this definitely suggests that things like "size" and "leaping ability" really don't age well. Far and away the majority of the guys who were still producing at 34 were short guys who got a ton of yards and not a lot of TDs. At the very least, I don't see any reason to believe that Smiff is likely to age less gracefully than, say, a Hines Ward, Chad Ochocinco, or Donald Driver.