Cows can easily reach the age of 20 years or more, but the longevity of animals is often artificially reduced by humans for breeding purposes.
Practically, there is no mathematical formula (well at least, not a simple one) because the age of a cow does not follow a linear curve compared with the human age.
So it's rather from observations of the ages of cows that veterinarians have established a correlation table (age chart) to see an equivalence in human age:
|Real cow age||1||2||3||4||5||6||7||8||9||10||11||12||13||14||15||16||17||18||19||20|
Life expectancy of the cow: a cow can live 15 to 20 years ... but too often it ends up on the plate before ...