Hi - welcome to aviation!
At 40 my recommendation is to keep your "well-developed, established and safe" career and pursue a life of recreational flying! It's very satisfying and there are plenty of options to choose your own adventure, for example formation flying, aerobatics, club flyins & tours. Or just smash the circuit area for an hour on Sunday before having some beers and talking aircraft with fellow owners (set aside an entire day!).
Plenty of people build their own.
Vans RV Series are very popular although there are dozens of others.
The Sports Aircraft Association of Australia (SAAA) have loads of members to provide help and advice on your build. Sports aircraft are wonderful: they do everything decent. Decent speed, slow takeoff/landing, decent cargo, good handling, light aerobatics, etc. Do your own maintenance if you built it.
You can buy one already built for $80-200k depending on the size / quality / engine / avionics fit out.
Operating costs are about 35L/hr @ $2.10 per L. Plus the odd $15 quart of oil. Hangarage roughly $200/month (varies). Insurance 2-4% of hull cost depending on experience & type (varies). Add $220 every 2 years for a security card (ASIC) if you intend to land at any security controlled airport (most regional airports). $100-200 a year for maps/charts. Flight review every 2 years: another $200-300 if you use your own aircraft. Aviation medical $300 (varies) every couple of years. Annual maintenance: $500-1000 if nothing goes wrong (varies massively - expect bill shock here!). Varying airworthiness directives: anything from $200-1000. Miscellaneous additional requirements to install new boxes in your aircraft, comply with CASA directives - [insert bill shock here].
If you choose an aircraft, my recommendation is to have one where you fill it up with fuel and can happily stick the docket in your pocket without looking at the bill.
If you have to analyse at the fuel docket, you can't afford it. Get something smaller.
If you're after something smaller, ultralight's are also popular. There's some advantages to ultralight aircraft such as dealing with the excellent RAAus (
https://www.raa.asn.au).
But saying that, I'm framing my answer around my life circumstances (family etc), not yours. If you're a free spirit, then the world is yours. Get a good instructor and learn to fly properly, then head to PNG, Africa, Northern Territory - go and see some crazy stuff that nobody will believe!