Within T8 international arrivals is located in a different area from all departures and both are exclusive to AA. The departures area is actually in 2 parts on either side of the aircraft stands but if you do need to go to the far building you walk between them underground all without the need to go outside. Unless your walking ability is restricted in some way I would say it isn't by any means challenging.
You will arrive at the lower level, clear immigration and re-check your bags before exiting into an indoor arrivals hall. As you do so you will see lifts and escalators up to "Departures" across the hall. You go 1 floor up and are then right in the departures area. You will clear security again before entering the Gates area. As AA control T8 any late international arrivals are met by their agents who will hand out the orange fast-track cards Martin refers to. You need to go to the far end of the departures security (which is quite poorly signed) to take advantage of that otherwise you will have to use the consistently long lines in the general gate entrance.
I used to transit JFK several times a month up to a couple of years ago and, like Martin, while I had a few close shaves I don't think I ever missed my connection. In the very unlikely event that happens to you I always found AA to be the most accommodating carrier in those circumstances so you really have little cause for concern.
(Just to add- if you are returning through JFK your domestic flight will arrive in the same terminal as your international flight departs from so a much simpler routine!)
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