Yeah, he was referring to Agility. If you want your Raichu to have max Speed, evolve it whenever you want, and maybe EV train it in Speed (Super Training).
In the episode of the anime where Ash's Pikachu battles the Raichu, Brock said, "Raichu evolved too fast, and it never learned the speed attacks it could only learn in the Pikachu stage!"
That's pretty much it. Hope I helped!