At the age of 40, earning 15 to 20k is not bad at all I would say. It all depends on the place where are you living and how much I spend every month, your financial education and so on. Some people don't even imagine how much money you can save by changing some habits, or doing other things differently. For example, you save very much money every month, on the energy bills, if you get a dual fuel deal, like it's shown in this guide
https://www.simplyswitch.com/energy/guides/understanding-dual-fuel-deals/. This is only one example, but there are way more tips which can improve your lifestyle by changing small things.