No, I don't think you're mad, but there's a few things to think about.
You're 40, at the moment there's a retirement point at 60/65 for *some* forms of professional pilot, it'll take you 3ish years to qualify, so that's in the order of 22 years professional career - longer if you elect to go into something like flying instructing later on in your career. So you're not too old. You are likely to take a bit longer to qualify than a 25 year old, but not obscenely longer if you are dedicated enough.
In my opinion you want to start with one really important thing. Do a PPL. This will give you much more honest answers than any amount of aptitude tests and enthusiasm about whether you've really got the ability and dedication to go through flying training. Pick a reputable local school, make it clear you're considering going Pro, put the effort into both the ground studies and the flying training. At the end of that, review your position from a far higher level of personal knowledge.
You don't have to go fixed wing, you could go rotary. You also don't have to become an airline pilot, there are other FW jobs such as air taxi, fishery patrol, instructor. Get knowledgeable about all the options. Join the British Women Pilots Association - they're great with support and information.
After that, if you're still dedicated to this - go for it. No, you shouldn't need to live away from home: there are suitable schools across the UK, most of them basically do professional training in office hours. So you don't need to abandon your home life with your child - just treat the training as a full time (or part time) job over 2-3 years, and you'll get there.
Regarding academic skills, A-level standard maths and physics / general science is perfectly adequate for professional pilot training, and there's plenty of material out there to help you brush up if you need it.
G