Not at all.
Well, it depends on the EVs of the Aerodactyl.
If your Greninja is maxed out in speed EVs and is Timid, its speed is 377 while a maxed out Aerodactyl's speed with a speed+ nature is a whopping 438.
The only way Greninja can outspeed it is if Aero has only 24 EVs in speed with a speed+ nature, or if it has 160 EVs in speed with a neutral or speed- nature.
Source: Checking numbers on PS
Hope I helped.