This season is Lukaku's fourth in the Premier League and second with Everton, having joined the Merseyside club permanently from Chelsea in the off-season, but there has been a sense the Belgium international has yet to live up to his reputation with just six goals in 16 league games.
Having broken through as a professional in the 2009-10 season with Anderlecht - scoring 15 goals in 33 league matches - Lukaku has been well known in European football for six seasons but remains just 21.
The powerful striker does not understand why he cops criticism when pundits and fans are so quick to give Barkley - who is also 21 - leeway for his youthful inconsistency.
"Sometimes I think people forget I'm still 21," Lukaku told The Mirror on Friday.
"They think I'm 25 or 26 because I've been around for a few seasons now.
"Sometimes, I look at Ross [Barkley] and think 'We're both young but people don't realise that'.
"I'm still 21, sometimes mistakes happen - things happen because you don't have the right experience. If I keep improving like this, then when I'm 25 or 26, that's when there will be no excuses."
Lukaku is the youngest forward Everton manager Roberto Martinez has used in the Premier League this season and the Belgian claims he is picking up a lot from the more experienced members of the squad.
Samuel Eto'o, 33, is a particular mentor for Lukaku.
"I'm picking up lots from him [Eto'o] and he has a tremendous football knowledge," the youngster said.
"He doesn't give me a yard. When I go to do finishing, he follows me across and says, 'It's you against me again'.
"He hates to lose and I hate to lose so when we are on the same team in the small-sided games, we never lose."
Lukaku says he also learns a lot from watching football - lots of football: "I watch a lot of games and in a week I can watch 10 games, easy.
"In Belgium, you grow up watching all the leagues - Germany, France, Spain, Italy, England - and I watch them all.
"I remember watching Bayern Munich v Man City last year and [Thomas] Muller was always running in behind, running in behind. He never got the ball four times. But the fifth time he did it - goal.
"I tried that in a game and the third time I did, I got it and scored."
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