I am noticing an increasing bias against folks in their late 30's and definitely 40's who don't have experience commensurate with age in the UK. Admittedly you need "less" hours compared to Australia but you need turbine hours for sure.
If you're not well on the way to being qualified and looking for work by perhaps 36, 37 at the latest then seriously consider flying for fun (UK). Of course, if you're independently wealthy, own your house and have a pension portfolio all sorted, then go for it.
Reason why. You've got maybe 20 or so years to "pay back" what you've spent plus continue saving for your retirement. I wouldn't be holding out for a Final Pension Scheme being in existance when you get into the airline industry. They are going slowly. By the time you're in your 30's you should be on good money. Chances are when you start with the flying career you definitely won't be on good money so that's a few more years of "catching up to do".
This assumes you do crack a decent job. If you don't, then it is a very expensive gamble, something your partner does need to be aware of when you decide to do this.
I am finally earning decent money after changing careers 10 years ago. I have ~20 years to save up enough money to retire on and buy a house. I have a great job, one I love doing. I'm not in an airline either.
I can say it's worth the gamble but I know of others the gamble hasn't gone their way.