Answer: Citrus trees can set up to 4 crops a year so what you describe is normal for your tree. Not all of the blossoms will develop fruit, but they sure are fragrant! Lemons take months to ripen. The only way to tell if they're ripe is by tasting one. If one is ripe, the rest of the crop of the same size and age should be ripe, too. Sometimes they drop from the tree when they're ripe; sometimes they hang on the tree for months after they ripen. A taste test is the only sure way of determining the ripeness.
Your grapefruit grown from seed will probably never produce flowers or fruit, but they're a fun project. I call this garbage gardening and I've grown citrus and apples from seeds. Never had them bear fruit, though.
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