Originally Posted by GBR
Why give up tee shirts - they are completely ageless.
If it's really f*cking hot, then a plain white tee is fine if you're just hanging out. I like the one's from Alternative Apparel and have a few. I also have a nice blue & white nautical striped tee and white & blue nautical striped tee from J.Crew, so if I have to go out in a tee, I can do so with a bit of style. Otherwise, there are better options ... particularly if you're a grown-up.
If it's short of 90 or so, a tight-fitting, well made polo is just as cool and looks a bit better. As does a linen short-sleeved shirt.