Steppenwolph hit it square on the head, Machine Ager. There are indeed some rules of thumb on these matters, but the proof is always in the wearing.
You might find, as I did quite some time ago, that you can indeed pull off a look you may have thought just wasn't right for you at all. There was a time I wouldn't wear a hat with a brim narrower than 2 1/2 inches and a band ribbon wider than 9 ligne (about 3/4 of an inch), and I generally preferred the brims wider yet and the bands narrower yet. In other words, I had several Stetson Open Roads and hats of that style (Mallory Dallas, Dobbs Westward, etc., etc.). But then some irresistible deals on vintage hats in other styles came my way and, well, you know how it is -- you get a "new" hat and you just have to wear it.