Harry Potter's Matthew Lewis on Girls, Growing Up – And Emma Watson
07/15/2011 AT 09:00 AM EDT
"In the early days, Neville [Longbottom] and I were not very dissimilar – I was a short, chubby, shy kid, just like he was," Lewis, 22, told PEOPLE about his screen alter ego at a Manhattan press junket for Harry Potter and the Dealthy Hallows: Part 2.
"As he evolved and matured, so did I," adds the actor – although he admits that he's still got a ways to go with the ladies.
"You know, girls in general are scarier than Voldemort," Lewis says with a laugh.
One who's less intimidating? His costar, Emma Watson.
"Emma is like my little sister," says Lewis. And he's taking the big brother role quite seriously: "We have to vet all her boyfriends to make sure they're good enough for her."