This may seem like a weird question but WHEN do you start to age a frog?

For example, Mija my bullfrog is 2 1/2 years old, or 5 years old.

If you count out of the water, no more tail, than she's 2 1/2. She spent 2+ years as a tadpole, which would make her older.

Any thoughts on which is correct, birth or metamorphosis?

Thanks