I'm suffering from a quarter life crisis (I'm 20.) I think a lot of people do. They just never talk about it.
It takes different things/approaches to motivate people. For me, inspirational speeches work really well or knowing that your manager is actually interested in your work.
However, it does sounds kinda odd that he didn't take the equity... He might just be an immature person that doesn't want to take responsibility. And this could be for various reasons completely outside the work environment that you have very little control over.
I think that just talking to him and asking what's up and what's going on is the best solution. Maybe he just needs a wake up call? The sincere, "I'm worried. What's up?" usually works pretty well?