It's got barge boards in front of the side pod. They weren't introduced into F1 until McLaren started using them in 1993. It's too "smooth" for a '91 car anyway. Those cars had fairly blocky sidepods, more of a straight-line drop on the nose (this one is curved) and much taller rear wings.
Indeed, the rear wing not being as high as the top of the roll bar is a big clue. If I remember correctly, they were part of the post-1994 rules, introduced after Senna's death and designed to slow the cars down. The smaller, lower, rear wing wouldn't produce as much downforce as the bigger, taller, ones would.
The 1994 Ferrari had a high nose with the front wing hanging from two pillars that dropped down from the nose, this car doesn't. That leads me to 1995, and the Ferrari 412-T2
Google Image Result for http://www.marksf1models.co.uk/Minichamps/Ferrari/950028med.jpg
OK, thats a model, but thats also the best picture of the car I could find
The stickers are all copyable, but they do match Alesi's car (27) and if you look very carefully, you can see a tiny bit of yellow on the tip of the nose, the same Ferrari badge you find on the bonnet of their road cars.