My ex-SIL has bipolar, and I have to tell you, I worried about her a lot. Frankly, I didn't even think she should have been allowed to drive a car. I certainly wouldn't want her flying an airplane. In fact, I wouldn't even want her being a passenger on an airplane if she was anywhere near the controls.
When she was on her medications, Liz was a sweetheart. She was one of the kindest, funniest, and most engaging people I knew. Everyone loved her -- when she was on her meds.
The problem is that many people with bipolar have this bad habit of thinking they're cured and stopping their meds without telling anyone, and no matter how many times this goes badly for them, they don't seem to learn from it. Liz is one of those people. And although I don't know if this is typical or not, when she went off her meds, she would seem fine for a while. And then all of the sudden, she would leap right off the deep end.
Her depressive episodes consisted of either inconsolable despair or seething anger, depending on what else was going on in her life (or sometimes what she merely thought was going on in her life). Similarly, her manic episodes consisted of either extreme happiness and reckless, daredevil behavior, or destructiveness for the sheer joy of it. For example, she would throw dishes and glassware against the wall, laughing hysterically as they shattered.
Liz's condition got her into legal trouble on several occasions. She would do irrational things like stealing stuff just for the sheer joy of it, and then giving it back, apparently thinking that the people from whom she stole it would share her amusement. They didn't.
Thanks to smart lawyers and compassionate judges, Liz never did more than a few hours in jail before being transferred to a hospital, and most (if not all) of her charges were ACD'd in the end. But she did spend quite a few stints in psych wards waiting for her meds to kick back in after these escapades. She would then swear to never stop taking her meds again.
Until the next time... there was, unfortunately, always a next time.
I haven't seen nor heard from Liz in quite a while. My break-up with her sister was less-than-amicable, and I suppose there are some bad feelings surrounding that. The last time I talked to her we had a pleasant conversation; but since then she changed her number, and she hasn't seen fit to give it to me.
I hope she's doing well. I have no hard feelings toward her, nor any reason why I would. She's a sweetheart. But she's sick. And as much as I like her, I certainly wouldn't want her flying an airplane.
In my opinion, OP is in a tough situation. Bipolar, I am told, is highly heritable; so there's at least a chance that the prospective student has, or will eventually develop it. On the other hand, there's no reason to believe that he has it now, nor any certainty that he ever will.
So from a strictly ethical point of view, I think I'd hope for a very long training period -- long enough to observe the student and become comfortable with his general stability over time. But I also would be careful not to read too much into normal moodiness, frustration over bad landings, and so forth.
The thing is this: The law is what it is, and at this point, it doesn't seem like there's anything disqualifying this student from a medical (or from flying SP). But from a moral and human decency point of view, if he is in fact bipolar, then I wouldn't want it on my conscience that I gave him another a means to kill himself -- and possibly take a few others along with him.
It's a tough call. I wouldn't want to be in OP's position, that's for sure.
-Rich