estimated age; probable age
Used in forensic, archaeological, or medical contexts to refer to an age determined by estimation rather than exact records. Often appears in news reports about unidentified victims or remains.
The estimated age of the body is believed to be in the 30s to 40s.
Determine the estimated age from the bones.
年齢 simply means 'age' (actual or stated), while 推定年齢 specifically refers to an age that has been estimated or inferred.
推定 means 'estimation' or 'presumption' in general; 推定年齢 is a compound noun meaning 'estimated age'.
Compound of 推定 (estimation) + 年齢 (age). The exact historical derivation is straightforward; both components are standard Sino-Japanese words.