Please don't panic, K Kacox ! All these test results/numbers have a range for "normal" and the only number here that's even slightly above the reference range is the creatinine... And as FeebysOwner says, lots of things can make a creatinine number a little high. It's worth asking your vet about that.I am sorry that we are causing panic - it isn't our intent. If we had gotten the lab results you just shared above, we would have told you before what I am about to tell you now.
BUN is affected by all sorts of things, slight dehydration, stress, to name a couple of the more typical ones. Creatinine can also be impacted by a few things - one of the most common is cats who eat high protein diets and have high muscle mass can typically have a higher creatinine count; slight dehydration can also elevate creatinine. The phosphorus number is superb. I actually think your vet wanting your cat on a kidney diet sounds premature, IMO.
I would just monitor the creatinine level (and all the others too) over time and see what happens. And, in the meantime let your cats eat what they have been eating as long as they like it!!!
I, too, would monitor the cat's results -- have an annual test as part of the annual exam -- and then see how things go. And let your cats eat what they want rather than forcing them on a kidney diet at a young age, when they really need that protein. If they're eating a lot of dry food but don't drink much water, it would be worth feeding them some/more wet food and/or adding a fountain or other way to encourage them to get more fluids.