It's a speed limit, not a target!
and the OP's attitude sucks.
There are plenty of reasons why somebody (of any age - not just the elderly) might choose to drive, or end up driving, at 25mph on a road that's got a limit of 30.
As someone who frequently cycles on such roads, or walks along beside them, I welcome careful, patient, non-speeding drivers, who are paying attention to their surroundings and road conditions (which could well include things like pot-holes, puddles, pedestrians, ponies, puddles...), and aren't filled with road rage and ageist assumptions.
The choice shouldn't be between 25 and 31. If the road is clear, and you feel comfortable going at a higher speed, why not stick to 29-30?!
Any decent driver really should be able to reduce their speed to match other road-users without ever 'slamming on' the brakes. I recommend that the OP considers improving their skills by taking an advanced driving course.