You are making the same mistake that the youngsters make. The airlines are not salivating at the prospect of frozen ATPL holders generally. Historically they have sought experience commensurate with the vacancies they are seeking to fulfill. This has been satisfied by career improvers and ex military pilots for the most part, with some (cadet) intake from approved and or affiliated training schools in small measure.
In recent years there has been an expanding industry of airlines and flight training organisations offering a mutually beneficial package of training leading up to a type rating and line training. This has had the effect of providing a stream of new and low cost first officers for some airline companies, and a fairly seamless fast track career progression for some trainees. These trainees would hopefully complete their probationary periods and be offered full time paid employment with either that same or another company. The problem of course was that this distorted the market for pilots. Career advancers and ex-military pilots were now competing for "jobs" that this rapidly flourishing "integrated" industry was turning out. Coupled with the economic turndown, and plentiful supply of applicants, the market has been oversupplied and prices (wages) have been significantly depressed.
The good news is that in fact companies cannot discriminate against you simply on the basis of your age. Of course they can discriminate (lawfully) on the basis of so many other factors, that it is almost irrelevant. Nevertheless age alone cannot be used as a reason for refusal.
With age comes maturity, and for that reason perhaps there it is a less appealing prospect to invest large sums of money into very risky and speculative ventures. Buying "jobs" may seem appealing at 19 or 20 when you may be more blinkered to the reality of what is happening around you and there is still 45 years ahead of you and few immediate commitments other than those you seek to embrace in pursuit of this career. At 40 you are likely to already have many other commitments and a far more cautious approach to risk generally. The airlines that have not embarked on this "pay to fly" concept (and they are becoming fewer,) are still constrained by the wider economy, and would still source their potential candidates from those with experience and at age 40 many similar applicants would have plenty of that experience.