C41 should have separate bleach & fix; combining them is a generally bad idea and any commercial lab will be doing them separately. However, the age of the film doesn't have any bearing on the effectiveness of bleach & fix.

If doing the film yourself, you could maybe extend the developer time slightly to make up for a possible loss of latent image, say to 3:45 or maybe 4:00. They should still scan OK but might be more difficult to make analogue prints if you do that.

I wouldn't bother adjusting the process at all. Just develop them as recommended.

Rinsing after developer is fine and will extend your bleach life a little, but doesn't really matter. Water makes a fine stop-bath. Don't use E6 chemistry, it's not the right stuff. Wrong dye couplers, etc, and you don't want reversal, etc.