I wouldn't say he'd get anywhere near 30 pounds but may well hit the mid 20s (I'd say that is probably very likely if he is just 7 months). As others have said, larger cavaliers are not unusual. I don't think it's that that hard to breed for the breed standard (breeders here can correct me!) but you do get odd genes showing through sometimes which some feel may be due to their being perhaps a larger spaniel like springers as part of the background of that particular cavalier line a long time back (it is said that springers were used in some lines when the breed was reconstructed in the first years of the last century). Or it may be that this was a breeder who wasn't really breeding for conformation. Unfortunately, it isn't very difficult to get the proper kennel club registrations or several-generation pedigrees -- lots of casual breeders can offer these and it is one reason why AKC (or equivalent, CKCSC too in US, IKC in Ireland etc) registration is only the very basic qualification for considering a breeder -- they need to be doing a lot more than =getting kennel club registration, so research is important (you can see what to look for in the Library section).
If you got your puppy from a breeder who definitely shows their dogs and/or is actively involved with the national or regional cavalier clubs and other dog sports, and if those pedigrees feature dogs from some of the known, good lines, then you either have just a somewhat larger cavalier (he may never grow much larger anyway and dogs a few lbs over breed standard are very common!), or maybe a throwback to some earlier large genes. If your breeder had no involvement with showing dogs and isn't active with her dogs in some professional way then the situation is very likely to be that this isn't a breeder who was breeding cavaliers for correct type and conformation.
If you got him directly from the breeder only recently (so at 6-7 months old) it may be she rehomed him because he was already clearly going to be over breed standard and therefore good for a pet home but not for showing or a breeding programme. Indeed the reason lots of under and oversized cavaliers go to pet homes is just that -- breeders hang on to dogs they know will contribute desired genes to their lines to produce potential show dogs that are also healthy and of good temperament. Very very few dogs are of that sort of quality that their genes are important to conserve. Lucky us that this is true as that's how we end up with beautiful dogs from good, health-focused breeders -- they go to pet homes.
Only time will tell what Bentley's final size is going to be though! As long as he's in good weight, that is what matters. Most boys will add a few more lbs though in the next few months and then maybe another lb or two until they are age 2-3, the breeders say -- hence that's why I'd guess he is most likely to end up around 23-25 lbs or so, but I'd doubt he'd reach 30. Most of their major growth is done by 6-9 months.
A lot of the rescue dogs I get in are a little to a lot over breed standard.
