40 years ago I chose to be a professional engineer and not an airline pilot. Partly because it was the mod seventies and there were no airline intakes and partly because I didn't want to work in a big company, controlled environment.
Watching other mates, it would seem to me that flying can still be a good career, but the path is no longer clear and will involve periods working in other countries and potentially with colourful employers. Especially with a late start. You're not going to fit the airline HR dept's template.
I would encourage you to think about the sort of life you want. At 35 from a standing start you're very unlikely to have a settled life in a capital city. Having been in the RAN you will have greater tolerance for a regulated environment than me, but the size & shape of organisation you want to work for would be good to consider.
Finally, I would presume that in the overall field of diving, your skills are near the very top. I assume that military dive training is rigorous that (like pilots) the lesser skilled will have been washed out by your age.
I'd investigate options for combining both interests. The first thing that comes to mind is tourism. But the mental picture I have of flying tourists to dive sites then supervising the dive is very nice. Compared with Australia there is a huge amount of scuba tourism in Asia. There must be mining niche's too, but I don't know what they are.