Drink now. Beers like Fantasia that have been aged with fruit are typically better when you drink them fresh.
Yep. Agree with this whole heartedly. While Fantasia isn't as puckering sour as a Fou' Foune or a Cascade Apricot (not peach based but still similar), the fruit character on Fantasia is big and shines arguably better. If you cellar it sourness will likely become more intense but the fruit will drop off. Enjoy the fruit sours/lambics fresh and grab some Geueze (Tilquin and 3F are available around town) to age into a more sour beer if you like.
Just had one last week at a tasting and it was fantastic. Insane peach nose and the taste right there with it. If you only have one, drink it now. If you have two...drink one now and save one
I should be getting one soon in a trade. You best bet I'll be drinking that one asap. Depending on how it is I'll try and get another bottle for the cellar.