He certainly sounds gifted. It’s hard to say if he has Asperger’s. If he does, it seems like he managed to overcome his challenges and make a life for himself. At 56, I’m not sure what benefits there would be in a diagnosis or if it’d be possible. The older you are, the harder it is to detect. Low emotional intelligence isn’t exclusive to Asperger’s, and many adult Aspies grow in social skills enough that Asperger’s can’t even be detected.
If you feel he still struggles with expressing emotions and reading others, I’d just suggest to him to work on that with books on social skills, a social skills class, or possibly a behavior therapist. If he is against it, it may be worth bringing up Asperger’s but I wouldn’t assume he has it just because he struggles with some socializing. Him struggling with eye contact does make it more likely, though.
For someone who seems unhappy and lost in life in his 50s, there would be a lot of benefit in reading and understanding Asperger’s. But, at the same time, they may be more stubborn and refuse the idea. This was the case with my dad. If you’re close and mention it in a way that doesn’t criticize him, it might do some good.