A pull-down shelf or a low drawer insert moves Dad's everyday items into easy reach without rebuilding the kitchen, but the install only holds if it is anchored into the cabinet box and not the door. Work through it in order, from the survey to the first service check.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Survey what he reaches for
Watch him work the kitchen for one day and write down what he reaches for above his shoulder, what he has to stretch for, and what he drags out of a deep cabinet. Those are the items to move. Do not move everything, because a shelf that holds the whole pantry is a shelf he will overload.
Check the cabinet before you buy
Open the cabinet and look at the box. Note whether the sides are solid wood, particleboard, or a thin panel, whether the cabinet is face-frame or frameless, and whether there is a rail or stile where hardware can bite. A shelf mounted only to the door will fail when the door is opened with weight on it.
Order to the cabinet you have
Order from the inside dimensions of the box, not the outside measurement of the door. Check the weight rating on the product page against the heaviest thing he will put on it, and ask the seller whether the hardware is sold for your cabinet type. If the cabinet cannot take the hardware, the next step is a cabinet installer, not a bigger screw.
Install and test
Mark the mounting points on the box, pre-drill, and anchor into solid material. Check that the shelf clears the drawer or door beside it and that its full range of motion is free. Load it with the real weight before you let him use it. Do not install on a cabinet with a soft or water-damaged panel, because the hardware will pull out under load.
A kitchen install like this does not need an electrician, but if the work involves moving a light, an outlet, or a vent, stop and call a licensed electrician for that part.
Service it after it goes in
Check the screws and the slide mechanism at an interval you set, such as every season, and clear any crumbs or grease that builds up on the track. Note any wobble, sticking, or noise and fix it before he uses the shelf under load. A shelf that stops moving smoothly is one he will start to yank, and that is when hardware fails.
The next move
Do the one-day survey this week, pull the box dimensions, and bring the weight rating and a cabinet photo to the store or the installer before you buy. For local help with the install or with finding an installer, the Local Help in St. Louis page is the place to start.