Heli_port - a cynical person might question whether any school's aptitude tests are entirely unbiased, seeing as their income depends on a successful result. GAPAN aren't trying to sell you anything, and if I recall correctly, they quite specifically brief candidates that no testing system is perfect, and a low score does not necessarily mean you'll never fly an airliner. That said, they have been around a long time, and between them and the RAF, I suspect they know a thing or two about aptitude testing.
If you make it to the airlines despite a low GAPAN score, then I'd be delighted for you and it's a story worth telling. Please don't give the impression though that independent aptitude testing is not worthwhile, it very much is. There are exceptions to every rule.
I have met one or two people during training (thankfully a small minority) who were quite obviously pouring money down the drain. Like the guy who had sold his flat to finance his dream, and was still struggling to trim the aircraft a month into his IR. It was heartbreaking to watch, and I suspect that deep down he knew the score, but was too committed financially to back out. Or the one who finally managed a fifth series pass at the CPL, and wanted to be an airline pilot to impress the ladies. I kid you not. Any commercial instructor could reel off similar stories.
"Never give up" is a worthy ideal, and is how most of us get there in the end. Just be aware that there is a little bit more to success than a bottomless pit of cash and a never say die attitude.