My son is three-and-one-half years old. Grammatically correct but so unnatural that no native speaker would use it.
Cut a piece of wood eleven-and-one-half inches long. Grammatically correct but too unnatural for a native speaker to use.
These 'X and one-half' patterns sound like the kind of sentences we hear from little kids still learning the language. I've noticed that when kids only have a few years under their belt (or diaper as it were), they seem very adamant that you acknowledge that extra half-year, and they are in fact two and one HALF years old, not two!
But then, I guess if you're only two or three years old, another 6 months does represent a substantial percentage of your total age.