A dealer simply orders tires from the Michelin distribution center - they have no control over what dates they get. Any dealer in your area is probably ordering from the same Michelin warehouse, so you run the same risk. However, IMO the odds of them being more than a 12 months old are very, very slim. 6-12 months is fairly common, though. If you are ok with that, you can probably go ahead.
The tire manufacturer makes them in batches by size. A popular size is being made all the time and will likely have a "fresh" date. A less popular size may be manufactured just once in awhile, e.g. every three months or maybe even just once a year.
Can you get a refund on the tires if you don't like the dates when they come in?