1) In the US, this post indicates illegal discrimination. I know you're anonymous, but you should be pretty certain that no real-world employee can find this post.

2) Hire him on a contract basis for a month or two. Pay him what you'd pay a senior dev of whatever age. Evaluate him on the progress of the product, and have a trusted external party audit his work (if you yourself aren't technical enough).

3) Stop thinking about discriminating on the basis of age.