Plant age plays an important role in determining the fruit quality but studies to determine its effect are rare in fruit crops, especially in citrus. The present study was carried out to evaluate the patterns of flowering, fruit set, fruit growth, fruit drop, fruit juice characteristics and yield in Kinnow mandarin trees of different bearing age at the new orchard of Department of Fruit Science and in the laboratory of Department of Botany, Punjab Agricultural University, Ludhiana during 2015-2016. There was a significant variation in the biochemical constituents of the fruit juice in the three age groups under investigation. The maximum total soluble sugars (8.82%), total soluble proteins (14.90 mg/100 ml juice), flavonoids (17.69 mg/100 ml juice), vitamin C (26.70 mg/100 ml juice), total soluble solids (10.40 %) and TSS: acid ratio (11.81) has been recorded in the fruits that were picked from 15 year old Kinnow trees. 15 years old Kinnow mandarin trees gave highest fruit yield due to decline in fruit drop and increase in fruit size.