Its been said here many times but theres no way you are too young to wear a jacket all of the time. I'm suprised you don't tuck your shirt in given your propensity for clothing. Like the esteemed Duck I am under 30 (just turned 26) and I wear a jacket almost everyday - more often than not I wear a suit and tie. Jump on in...I'm visiting my parents over the Winter holiday and, while having a discussion with my mother about my recent romantic prospects, got on the subject of my sartorial sensibilities.
I generally wear plain front, cuffed khakis, an OCBD (in white, pink, light blue, or french blue), a nice pair of shoes (must wear socks with loafers--sensory issues), and a belt. I often don't bother to tuck the OCBD in, and I almost never wear a jacket.
I indicated that I probably ought to wear a jacket on a daily basis, or at least more often, and she insisted that I'd look like an "old man" if I began doing so.
I'm a few years under 30; I'm not exactly in my teens and while I may indeed still be on the young side, I don't think adding a jacket to my ensemble would make me seem too old.
Then again, this is the same woman who objects to my fondness for argyle socks.