Cadillac, General Motors Co.’s luxury brand, is studying seven new model concepts to lure new buyers and build on the fastest sales growth among premium carmakers, two people familiar with the plans said. The brand has looked at a small sport-utility vehicle, a large flagship sedan, a subcompact car to rival Bayerische Motoren Werke AG’s Mini Cooper, and a Cadillac version of the Chevrolet Traverse and Buick Enclave SUVs, said the people, who didn’t want to be named because the plans are private. Cadillac is studying the models after sales rose 35 percent last year, topping all luxury automakers, led by the SRX sport- utility vehicle and the CTS coupe. The brand is seeking to ease reliance on those models, which accounted for 66 percent of its deliveries, and lower the age of its average buyer from 62.