@Arya: Absolutely not, in my opinion! Personally, I think that as long as the two cats in question are fully mature adults (20+ moons), then almost any age gap can be forgiven. The only time it should matter is when the cats in love were mentor and apprentice, in which case I think no relationship should be acceptable due to the imbalance in power.
So, I'm starting on my post right now, and the plan is going to be this: the day is normal, then badgers attack! Several cats are injured, two cats die and Honeystar loses a life, and three cats (including Honeystar) end up with an infection. I also realized, as I was writing the post, the several apprentices are going to be going to the Moonpool soon, to speak with their ancestors... Poor kits. Emotional upheaval and all.