I'm 28 going on 40... (because of my job)
I can see where the folks saying "X is too young" are coming from. I look back on how I valued things in hs and even college, and man, it's just crazy in retrospect. Something that was the center of my world back then is just totally irrelevant and not worth the time/energy/money. If I could take back the money I spent on things that I didn't need at the time, I could have gotten a half dozen iPhones...
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Ok let's talk turkey. I don't think the iPhone is really worth it's cost right now at all (yes, I have one, I consciously paid the early-adopter tax because my current phone was horrible, I do need a lot of the internet and extra features, and the timing on my cell contract was right). Within a year or two at the max, the price will drop for a more powerful and capable revision of the iPhone. I remember the first gen iPods costing something like $400 at the low end, and that was just 5 years ago. Now they're half that, for more storage, stability, and features.
If you wait for even just the second revision to come out, you will have a better phone for cheaper (and which everyone who bought the first gen will want really bad). If we wanna talk maturity, that would seem to be the mature thing to do.
Just my $0.02.