I won't smoke em' younger than 1 year old now......i've made that mistake before, and I've had more bad experiences than good.
If you can wait 2+ though, that's where they really come into their own...at least IMO.
I smoked a 10 year old FFOX I got in a trade from AR (thanks again Angelo!), and damn if that wasn't one helluva smooth, mellow, creamy smoke. Really had toned down, but the flavors were just awesome.
Best advice I ever got on Fuente Holiday stuff...
Age the Opus, and smoke the Anejos (fresh or whenever...they're good to go from the jump).