Predicting long term sequellae of chronic low back pain is little more than a guess. On the other hand, you could have a stroke and be suddenly incapacitated 30 seconds from now.
But the real issue with your back is sudden incapacitation. An acutely herniated disk could do that, but chronic back pain - unless it progresses to the point where you are incapacitated by spasm, generally does not.
In that respect you might actually be better off flying a two pilot aircraft. There is actually a reasonable amount of data concerning sudden incapacitation in the airline business - mostly due to heart attack or stroke - with pretty benign results, at least for the passengers. And yeah, you could turn the controls over to the other guy and get up and stretch a little.
The real issue is do you want to take the chance of investing in a career that may become too painful for you to continue in. That’s a definite - but almost impossible to quantify - risk.