Ahem...
Oliver Queen, aged 27 (his birth year is stated to be 1985) played by Stephen Amell, aged 31.
Thea Queen, aged 17 played by Willa Holland, aged 21.
John Diggle, maximum age 36 played by David Ramsey, aged 40.
And these are the ones whose ages are either confirmed or sussable from the dialogue. As you can see, neither the characters nor the actors who play them 'skew young', as you so describe. Even the youngest character on the show is aged 17, pretty old as far as 'kid sister' side characters go. Likewise, all characters are played by actors a little older than them. The only one who's a little young is the police detective who's aged 43; which is slightly young to play the father of a woman in her mid-twenties.
Congratulations. You've identified a love triangle; one of the oldest and commonest relationship archetypes in both, fiction and real life.
Now, onto something more positive:
I will conceded that the acting isn't top notch. However, it's certainly adequate - especially relative to everything else out there, particularly the CW - and suffices for the story's current complexity. Moreover, the action is certainly well above average. Choreography is pretty complex and the camera stays on it, rather than being short cuts spliced together.
Also, anyone else really digging Diggle (the bodyguard)? I feel the guy really came across as badass this episode; going toe to toe against the supervillain of the episode. Between his badassery, his military background and propensity for guns, as well as his getting closer to Ollie's secret, does anyone else think/hope he's the show's Arsenal/Roy Harper?