At our age (I am 48), your high throwing may simply be a low throwing
elbow. The proper position for your elbow is at least shoulder height
from the high cocked position thru ball release. Us "older"
athletes tend to get the elbow to the proper height at the high
cocked position, but we have a difficult time keepin it that high througout
the entire throwing sequence. Video is best, but a friend watching you should easily be able to see this. Ask him to tell you where your elbow
is in relation to your shoulder at about the time your shoulders square
to the plate. This is called “sailing”. You have seen many a little league
shortstop fumble a ball, hurry the throw, and “sail” it 10 feet over the head
of the first baseman because he never let his elbow get to the proper height. Fix this first (stretch and stretch again) before you worry about the fact that you are throwing inside. The “inside” throwing is probably a simple alignment adjustment,
that may take care of itsef once you get the ball down.
I envy your courage, good luck, and If you have known what I just said
for twenty years, i apologize.
Keep it simple: Balance, Posture, Alignment