Welcome! We're glad to have you with us, and feel free to ask any questions you might have.
I had the same experience you did when I started out, and I didn't even have the excuse of a childhood shoulder injury (though I do have mild scoliosis). It's not uncommon for fencers starting out to have tight shoulders and to rush to attack. Feeling right of way is not a natural skill, and some fencers never feel it (and make a virtue out of that by becoming excellent epee fencers

). (Don't mind me, I'm a sabre fencer.)
The remedy is partly more experience, and partly drill. If you practice hitting, say, a tennis ball hanging from the ceiling at target height, and concentrate on keeping your shoulders down and relaxed, it will eventually translate to your bouting.
I'm still working on that particular problem, mind you (and it has been ten years).