I think replicas mature faster only because they have the brain capacity for it, but as I've often noticed, age doesn't reflect maturity, but it damn well helps. When you've got years of experience built up you become (hopefully) more mature and intelligent, willing to look at things from more perspectives.
Or at least that's what happened with me. Regardless, it was also the view Namco wanted us to take. Since Luke is the hero and we see almost everything from his point of view, it's natural we're more sympathetic with him then the rest of what the group is feeling, even if he is whining and we know he's in the wrong.
As far as I'm concerned, the decisions he made after Akzeriuth and the actions he took from that point onward were extremely mature for a 7 year old, even one so matured as he. However I do agree with a great deal of your thoughts. On a side note, more picture time.
Have some Sync and Ion, I exhausted my Luke supply.