I'm guessing you've probably had this conversation with him many times. I would also guess that you have probably already tried really listening with a sympathetic ear, as most of us would for our spouses. If this happened 25 years ago, it seems safe to say that the subject has come up a few times and you probably really tried to be there for him the first 5 or 10 times he mentioned it. If that's the case, there probably isn't much more you can do. We all have something in our past that comes to the surface now and then that can really bum is out. That's normal! However, most of us also learn coping mechanisms that help us "shake it off" and get back to the joy of living.
If you've never really listened with a sympathetic ear, maybe it's time. Remember, this isn't about you trying to understand him. You can't. I mean, unless you have also tried to make the Olympic Team, you simply can't understand what he went through, the intense preparation, the emotional disappointment. Very few of us have any clue what that's like. That doesn't mean you can't listen to what he is saying and feeling.
My husband is a recovering alcoholic and has been for over 20 years. I've only known him for 10 years. I have absolutely no clue what it's like for him. I do my part. There is no alcohol in the house. I read labels and never cook with anything containing alcohol (contrary to popular belief, the alcohol does not all cook away). I listen to his frustrations and support the things that he needs to do for himself - the projects that he has found helpful in relieving stress rather than drinking.
He can never have a drink again because, simply put, he would want just one drink. I don't get it at all! One drink (ok, maybe 2) would be plenty for me. After that I just want to drink lots of water and sleep. How can you want more than 1 or 2? And of course he would say, how can you want just 1?
Long story, sorry, but my point is, you can't understand. You just can't. You have to accept. You have to come to a point where you can accept that whether it makes sense to you or not, this is what he is feeling and this is what he is going through.
My Pastoral Counseling professor said one of the first rules in counseling is to always accept the fact that the person you are working with is doing the best they can with what they have.
I think you have to try and stop focusing on what it is that is upsetting him (as ridiculous as it may seem to you) and just focus on the fact that something is upsetting him and he needs you to listen and care.