The famous plant breeder Mr. E.M. Savage, from long experience in growing citrus seedlings in central Florida, estimates that the time usually required for seedling trees on their own roots to flower is about as follows:

Mandarins 5 to 7 years
Sweet Oranges 6 to 7 years
Grapefruit 7 to 8 years
Tangelo 5 to 8 years

Occasional seedlings, especially those of grapefruit and tangelos, may require considerably longer periods. Savage grew a tangelo seedling that fruited for the first time at 22 years of age. All parts of the citrus tree do not pass through the juvenile stage into maturity at the same time. The trunk of a thorny seedling and the proximal portion of its main branches retain the ability to produce thorny shoots. As a seedling tree grows higher, the branches begin to show a tendency toward progressive reduction in thorniness, and an increase in flowering. The long delay of citrus seedlings in coming into bearing, is a serious handicap to rapid progress in citrus breeding. The above times from seed to fruiting can be approximately cut in half, by growing citrus trees year around in a tropical greenhouse. - Millet (1,269-)