Shadow Milk Cookie does not have an officially stated “age” in years in Cookie Run: Kingdom. Instead, his lore presents him as an ancient being created by the Witches at the very beginning of the Cookie World, making him canonically extremely old and effectively timeless.

In real‑world terms, you can talk about his debut age instead:

  • Cookie Run: Kingdom launched in early 2020, and Shadow Milk Cookie was introduced later in the game’s storyline and events.
  • Because he’s a fictional character, fans sometimes casually say he is “about a few years old” based on how long he’s been in the game, but this is just fandom language, not canon age.

Lore-wise, what matters more than a number is that:

  • He was one of the Witches’ original “Beast” Cookies, made to oversee knowledge and guide the world.
  • This places him at the very start of the Cookie timeline, far older than ordinary Cookies like Pure Vanilla Cookie and the students of Blueberry Yogurt Academy.

So, if someone asks “how old is Shadow Milk Cookie?”, the most accurate answer is:
He’s an ancient, primordial Cookie created at the dawn of the Cookie World, with no official numeric age given.

TL;DR: There is no confirmed number of years; he’s effectively ageless and extremely old in canon, and a relatively recent addition in real-world release terms.