"K18" meaning in Finnish

{
  "etymology_text": "The initial letter of kielletty (“prohibited, forbidden”) + 18.",
  "head_templates": [
    {
      "args": {
        "1": "fi",
        "2": "symbol"
      },
      "expansion": "K18",
      "name": "head"
    }
  ],
  "lang": "Finnish",
  "lang_code": "fi",
  "pos": "symbol",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Finnish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Finnish symbols",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "Alternative form: K-18"
        }
      ],
      "glosses": [
        "Age rating: not suitable for children under 18 years of age; mostly equivalent to NC-17 (US, motion pictures), 18 (UK, motion pictures), 18+ (generic)."
      ],
      "id": "en-K18-fi-symbol-pTlpesVg",
      "links": [
        [
          "NC-17",
          "NC-17#English"
        ],
        [
          "18",
          "18#English"
        ],
        [
          "18+",
          "18+#English"
        ]
      ]
    }
  ],
  "word": "K18"
}

{
  "etymology_text": "The initial letter of kielletty (“prohibited, forbidden”) + 18.",
  "head_templates": [
    {
      "args": {
        "1": "fi",
        "2": "symbol"
      },
      "expansion": "K18",
      "name": "head"
    }
  ],
  "lang": "Finnish",
  "lang_code": "fi",
  "pos": "symbol",
  "senses": [
    {
      "categories": [
        "Finnish entries with incorrect language header",
        "Finnish lemmas",
        "Finnish symbols",
        "Finnish terms spelled with numbers",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "examples": [
        {
          "text": "Alternative form: K-18"
        }
      ],
      "glosses": [
        "Age rating: not suitable for children under 18 years of age; mostly equivalent to NC-17 (US, motion pictures), 18 (UK, motion pictures), 18+ (generic)."
      ],
      "links": [
        [
          "NC-17",
          "NC-17#English"
        ],
        [
          "18",
          "18#English"
        ],
        [
          "18+",
          "18+#English"
        ]
      ]
    }
  ],
  "word": "K18"
}