If your family responsibilities don't prevent you from going away for ~5 months for the initial training (depending on MOS), then it's not utter madness to join at 40 if you're in decent shape.
It may be a pride-swallowing experience at first. You'd be thrown into a barracks with a lot of 17-20 year olds and you'd be treated like one of them. We had a 35 year old in my basic training. The trainers gave him only a tiny bit of slack.
You'd also spend some time as a 40 year old private - which might get you some looks.
Whatever you do, pick your MOS carefully. Look around and see what type of reserve and guard units are local because that's going to dictate your job choices. If there's nothing but infantry locally, then you're going to be infantry or something that supports them. If that's the case, be a medic. Everyone likes the medic.
It may be a pride-swallowing experience at first. You'd be thrown into a barracks with a lot of 17-20 year olds and you'd be treated like one of them. We had a 35 year old in my basic training. The trainers gave him only a tiny bit of slack.
You'd also spend some time as a 40 year old private - which might get you some looks.
Whatever you do, pick your MOS carefully. Look around and see what type of reserve and guard units are local because that's going to dictate your job choices. If there's nothing but infantry locally, then you're going to be infantry or something that supports them. If that's the case, be a medic. Everyone likes the medic.