Starting from scratch over 40 is probably pushing the limit if you want to go commercial. If you want to get into a jet I would say that you are going to find it very hard. The Air Force don't have age limits for no reason.
The other factor to consider is how on earth you are going to survive on the money on offer. If you are not independently wealthy or single you are going to struggle. On that note anyone of any age with a family is going to find Regional airlines and GA pretty tough financially.