Yes, you are right about the voice - Ciaran Kellgren sounded like a teenager, not a child. Unfortunately, it seems the 2003 movie has set the tone for putting more emphasis on first love/sexual tension between Peter and Wendy in any interpretation. Peter is hardly ever now portrayed as a naughty, selfish, impetuous - but brave - boy, but more like a cocky adolescent.
Going back to Peter's costume, I was intrigued to find that it's quite possible he was dressed in red (complete with red tights) in the early productions, rather than green. Of course, you can't see it from the b&w photographs, but the first picture books published in colour always showed him in red: the 1914 edition illustrated by Alice Woodward, Flora White's ABC in 1914. There's also a beautiful wax figurine of Jean Forbes-Robertson as PP from the 1920s in a red costume. Mabel Lucie Attwell seems to be the first one to illustrate him in green in a book, followed by Gwynedd Hudson's glorious illustrations of the 30s. Does anyone have any information on this? Are there any contemporaneous reviews that mention colour?