Marrying off a ketana

The Gemara in Nida on 66a tells a story of Ravina who married off his son to a girl from the house of R' Chanina. The story says that R' Chanina thought that in this instance they didn't have to wait 7 days from the time of the agreement to marry because she was a ketana. Ravina corrected him and told him that even for a ketana you must wait 7 days.

Ravina was at the end of the Amoraic period so why were they still marrying off ketanos. The gemara in Kiddushin on 41a says that R' Yehuda said in the name of Rav that people should no longer marry off their ketana daughters. Tosafos there says that ruling no longer applied in his days because of the problem of marrying off girls but was it already ignored in the days of the later Amoraim?

UPDATE (2/23): I saw this morning that the Aruch Laner asks this questions and says to look at what he wrote in Yevamos but I couldn't find it.