Sage Pulastya is not referring to Kartikeya or his followers by Kaumāra here. He is referring to one of the creations of Lord Brahmā.
In the Viṣṇu Purāṇa first aṃśa (Viṣṇu purāṇa is divided into six parts and are called aṃśa) chapter 5 gives the details how Brahmā created this world and beings.
There are nine creations done by Lord Brahmā namely Mahat, Tanmātra, Aindrīya, inanimate objects, animals, gods, men, Anugraha, and Kaumāra.
The first creation was that of Mahat or Intellect, which is also called the creation of Brahmā. The second was that of the rudimental principles (Tanmātras), thence termed the elemental creation (bhūta serga). The third was the modified form of egotism, termed the organic creation, or creation of the senses (Aindrīyaka). These three were the Prākrita creations, the developments of indiscrete nature, preceded by the indiscrete principle. The fourth or fundamental creation (of perceptible things) was that of inanimate bodies. The fifth, the Tairyag yonya creation, was that of animals. The sixth was the Ūrddhasrotas creation, or that of the divinities. The creation of the Arvāksrotas beings was the seventh, and was that of man. There is an eighth creation, termed Anugraha, which possesses both the qualities of goodness and darkness. Of these creations, five are secondary, and three are primary. But there is a ninth, the Kaumāra creation, which is both primary and secondary. These are the nine creations of the great progenitor of all, and, both as primary and secondary, are the radical causes of the world, proceeding from the sovereign creator.
The translator adds explanation to all the terms. For Kaumāra creation, he adds:
We must have recourse here also to other Purāṇas, for the elucidation of this term. The Kaumāra creation is the creation of Rudra or Nīlalohita, a form of Śiva, by Brahmā, which is subsequently described in our text, and of certain other mind-born sons of Brahmā, of whose birth the Viṣṇu P. gives no further account: they are elsewhere termed Sanatkumāra, Sananda, Sanaka, and Sanātana, with sometimes a fifth, Ribhu, added. These, declining to create progeny, remained, as the name of the first implies, ever boys, kumāras; that is, ever pure and innocent; whence their creation is called the Kaumāra.
Hence, the term Kaumāra refers to the creation of Rudra by Brahmā and also the mind born sons, four Kumāras namely Sanatkumāra, Sananda, Sanaka, and Sanātana.
Hence the phrase "acquireth the status called Kaumara" means the person who lives on vegetables or fruits means that he would take get the status of Kumāras.