Why adults act as teenagers?

[Red Ranger 1]

Isn't Martha still younger than Duncan despite being born before him?I think they aged Duncan up three years, making him 23 now, he was in the same year as Kirsty.(Although they might have deaged him when he came back in 2004, it was all a bit vague...)

They made him the same age as Kirsty, Nick and Jade in 2000, which would make him 23 now, but then de-aged him in 2004 to be the same age as Tasha and Ric, which would make him 21 now, but I reckon his age was probably changed again to make him older in 2005 . He was born after Martha though, so who knows what age he is actually meant to be now.

I know he seemed to spend most of his time with them but did we ever see Duncan in classes with Robbie, Tasha and the others?There was that leadership/paintball thing but that might have been a mixed age outing and he was actually in Year 12.Having characters' ages the wrong way round isn't exactly unprecedented in the soap world, EastEnders famously made Courtney older than Ben despite being born after him when they brought her back a few years ago.