To be honest, starting at 45 means you will be 48 by the time you complete the basics and will have zero experience. To an airline this represents a training "risk" as your conversion and line training will almost certainly take longer. Whilst advancing years may help with CRM issues, they can also be an obstacle to learning and over the years airlines have developed policies to take the "most likely to succeed in the shortest time" approach. While some airlines are happy to have career FOs, and indeed some senior FOs at companies like BA earn more than Captains, this is not the case with gulf carriers. FO on business jet may be an option, but for your peace of mind I would forget the mainstream carriers.