عمر بيولوجي (مصطلح)

is the age that most normal people would be when they have a body and mind similar to yours

Telomeres length could be used to measure it generally
We actually start Ageing since we are a fetus inside our mother's uterus. We continue to age after being born some cells stop division temperorily while other continue to have serial divisions to repair any damage through life.
Cell division is a finite phenomenum as stated in the Hayflick principal.

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