Just want to throw my piece out here, that whilst I'm not aware of what those in charge of hiring are physically saying, I am aware of 2 co-pilots (having between 200 and 300 hours total) over 40 getting jobs at 2 different North Sea operators. Whilst the older of the 2 is "only" 44 and you would likely be 46 by the time you've completed your IR, I don't think it's too late.
Your best bet is to reach out to those in charge of hiring now and ask them the question yourself.