My 7-m.o. baby can now drink fruit juices except for calamansi as per pedia. Why not calamasi? It has tons of vitamin c.

Calamansi and other citrus fruits should be avoided till baby turns 1. Apparently, citrus fruits are allergy triggers, like egg whites, and should be avoided till baby is older. So citrus based juices like calamansi juice and orange juice, it's better to hold off. Consider giving baby apple juice instead, it's a safer juice alternative.