A 5400 yd course is not that short for gents driving it 160 yards considering the approach shot lengths they are going to be faced with on Par 4s. Also, for the course you are referring to I estimate the Par 4s have to average longer than 260 yds, because the Par 5s are 800 yds or so, and if there are four Par 3s averaging 130 the total is 1320 yds. This leaves 4080 yds remaining for 12 Par 4s. That is an average of 340 per hole.
Anyway, if there are super seniors driving it only 160ish and breaking 80 consistently, they must be elite/exceptional in other aspects of their games. I play a lot of golf with 65-75 yr old seniors on a 5400 yd course. They all drive it 180-200 or so, but many are slicers and poor iron players. None can break 80.
I am 66 and drive it 200 yds. My average score is 76. On that course my average approach shot on Par 4s is 125 yds. The ten Par 4s average 313 yds. By that comparison the 160 yd driver of the ball would have 165 left when attempting GIR on those holes.