Our youngest of 5 turned 10 in January. This summer was her first diving. The shop is on the beach with a walk-in to 8' deep being a gentle grade. She could swim almost before she could walk! But that was always underwater, with her eyes open. We have a small neighbourhood pool that is < 100 yards from our house. The kids practically live there in the summer, and it's mostly less than 10 families there at any one time. She loved to be in the water, had no issues as a baby with getting her face wet or holding her breath. By 18 mo old she was swimming underwater, coming up for breath, and then continuing to swim underwater. We did nothing other than being at the pool most days and having her in the water with us. We see other parents trying to coerce their kids and almost force them in to the water when they don't want to be. It rarely works and usually ends up with a child that doesn't want to even be at the pool because of the negative emotions they associate with it.
We eventually got her snorkeling gear, and I made a similar mistake and "over encouraged" her. She kept swimming but wanted nothing to do with snorkeling for a couple of years. This year she snorkeled because she wanted to, and then started diving, because she wanted to. We had a fabulous instructor that made every aspect of the learning process a kind of game. She took to it so easily. Her first dive has video of her doing somersaults!! The instructor played games with swapping regulators etc.
Some kids take to it sooner than other. Just the way it is. A way to almost guarantee failure though is to try and force the pace or over encourage. Make all aspects of learning to be safe in and around water fun and let them go at their own pace. When they want to do something, then teaching them to do it properly and safely is so much easier!!