The phrase "age was based on" is correct and usable in written English.
It can be used when discussing how a certain age or age-related classification was determined or calculated.
Example: "The age was based on the year of birth provided in the application."
Alternatives: "age was determined by" or "age was calculated from".
The diagnosis and gestational age was based on ultrasound in less than one third of the cases although not routinely used for threatened abortion.
Gestational age was based on last menstrual period and/or ultrasound-based estimated date of conception.
Evans wanted fervently to believe that the Minoans' wealth in the late Bronze Age was based on a powerful seafaring empire that extended to mainland Greece.
The political economy of the analogue age was based on the idea that people would have secure, full-time employment that would enable them to save the deposit on a home relatively quickly.
Leather sandals of a similar age to the Armenian shoe were found in Israel's Judean Desert, but their age was based on other artefacts in the so-called Cave of the Warriors rather than on the sandals themselves.
Gestational age was based on menstrual dates or ultrasonographic biometric parameters.
Gestational age was based on the last normal menstrual period if confirmed (± 1 week) by early ultrasonogram.
Assessment of onset age was based on patient retrospective recall of the first occurrence of a syndromal hypomanic, manic, mixed, or major depressive episode.
Gestational age was based on first trimester crown-rump length measurement in line with national policy in the UK.
Gestational age was based on the date of the last menstrual period and on ultrasonographic findings during the first trimester of pregnancy.
The decision for a single dose schedule at 14 months of age was based on epidemiological, programmatical and economical reasons [2].
