Genetic LP is just that Genetic, and usually shows up in both knees, to one degree of severity or another.
As well your pup can acquire LP due to accident, trauma, or repetitive injury. Especially jumping off of high places when they are young and their bones have not matured yet.
Proper exercise is a must for all dogs, but especially if you want to keep their joints in good shape. Walking is great. At this point 4.5 mths old your pup should be able to do a moderately fast pace walk for 20minutes -2x per day. that is moderately fast paced for your pup and not for you
Next is to maintain a healthy weight. Puppies should have a wee bit of fat on them, but not a lot!. As adults the dog should have a discernible covering of skin over the ribs, a visible waistline, and their spine should not be too prominent to touch/pet.
Swimming at any age, is another ideal exercise. You can use your bathtub in wintertime, and a kiddy pool in summer. Get a lifejacket at least initially as it will do a lot to help your pup be confident and to use all their limbs correctly in the water.
Sit/Beg/Stand is an exercise that is amazing for rear leg and back strength. As a pup, just start with sit, a good sit, and have them stay in that sit for about 2 minutes from time to time. Give them solid stable surfaces to work on, and introduce the beg. After your dog is 14-18 mths old introduce the stand part.
Chasing toys and balls. First warm up your pup prior to introducing any of this type of play. It could be as little as a 5 minute walk. Or have them, follow you around the house at a walk, going up n downstairs.
Then if you want to throw the toy, do it on non slippery surfaces - your backyard - on a non slip mat indoors, or on a rug. Then after play, cool down your pup - walking - massage - stretching.