Too old to train for what? A good bird dog has the breeding in him, all you are doing is training him to maximize the use of that. A good lab will have retrieving instincts regardless of what level of training he has or hasn't had. You can't train him to use his nose either, he'll have one or he won't.
Through training and exposure, they learn how to use their nose to locate birds. Kind of like a beginning hunter learning to read a track. After a while you see stuff without even thinking about it that new hunters would miss. Same thing with your dog.
You can develop instincts, but you can't instill them if they aren't already there.
What's the worst that could happen? You don't have a dog now, so you'll be no worse off.