I have just read your post, so I'm sorry if my reply is a little late.
My Daisy did not have her first season until she was almost 2yrs old. Her next season was approx 9 months later. I let her have 3 seasons, and then she was spayed at almost 4yrs of age. She was spayed in the middle of her cycle.
I would definitely say "wait" and don't be pushed into it. I always take the Vet's advice with great interest, but have to remember, at the end of the day, that they are running a business. My Vet advised me to book Daisy in for spaying when she was only 8 months old. I said that I was thinking about having a litter from her and wanted to think about it. I also pointed out that with cockers, they really are late bloomers and need to have their first season, at least, before considering being spayed. But until I said that, I was very much given the "hard sell" about cancer, etc. And I know many cocker owners who have been encouraged to spay their girls before the first season.
If there's no medical hurry to do so, I would definitely wait and take your time.
Good luck!