Are you still submitting to other agents? I mean, is this an exclusive?
If it is an exclusive, then yes you should definitely nudge (at least I would). If not, then I would focus on sending to other agents. If/when you get an offer from another agent, then let Jason know.
In your case, he clearly has your manuscript, and it is in his pile of to-be-read-or-considered. In my experience, nudging doesn't necessarily make someone respond faster, and taking a long time might be because they are torn about the manuscript itself (at least that was my case when agents had my MS forever).
In sum, my advice is to treat your queries/partials/fulls like fire-and-forget missiles (at least as much as that's humanly possible).