Scholes questioned whether his former United team-mate had already peaked, despite the 28-year-old netting 19 goals in all competitions in 2013-14.
But Gerrard backed Rooney, who has entered the past two FIFA World Cups with injuries and failed to net at both.
"Paul Scholes is wrong. He's been Manchester United's best player at home and in Europe. He’s been in terrific form," Gerrard said.
“What I’ve seen from his performances in the United team, his form has been really positive.
"He’s in a better frame of mind going into this tournament than he’s had going into previous tournament when he’s had injuries."
In a column for Paddy Power, Scholes said: "There's a chance he's worn out.
"Wayne's peak may have been a lot younger than what we'd expect of footballers traditionally. Age 28 or 29 has been the normal 'peak'."
England face Uruguay, Italy and Costa Rica in Group D at the World Cup.
