HiFranc
First off, my disclaimer. I'm not a professional pilot, so take or leave my advice. I have however, been flying since the mid 80's and have often looked at going pro ... but haven't (yet).
So ....
Not trying to widdle on your fireworks, but I think you may be on the edge of a slope you really don't want to slide down!
I kind of think from your posts that you may know this already, but perhaps want to keep the dream alive? There's nothing wrong a with dreaming, but in reality you need to at least put your toe in the water before you leap.
Before anything else, find out if you actually like to fly! Don't worry about the fear of heights, it's something many pilots suffer strangely enough (I'm one! If I stand "or rather crawl" to the edge of a cliff I feel distinctly uncomfy! but stick me in a box with wings and I'm fine). If you get past this stage, you may fall so deeply in love with flying that all those other questions go out the window anyway, so problem solved! If you find yourself ok with the flying, but still unconvinced about the career change, then you have to be more logical in your approach and ask why you really want to do it? Still thinking it may be a good idea? Then here's a reality check .... Whilst you certainly aren't too old, you are not at the most attractive age to airlines. The asthma, may be ok? but again, it's another little thing that puts you behind the next candidate. These things may not be barriers to someone who's determined enough, but that's why I said earlier that if you fall in love with flying then your questions are answered.
They, and your other concerns are real though, so think hard and do at least get some real flying in (perhaps a PPL) before getting a loan and paying out for a "Zero -ATPL in three easy steps" course!
SS (non professional pilot but very professional dreamer myself
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