v'hu she'odan bo

R' Yosi B'reb Yehuda on nidda 46a says that a child who grows 2 searos (hairs) between the age of 9 and 12 is considered a gadol. The gemara qualifies that by saying "v'hu she'odan bo." Rashi explains that if it's still there when he turns 13 then it is "iglai milsa" that it was not shuma but really 2 searos to consider him a gadol. What does that mean? Does it mean that he was really a gadol from the time that he grew the 2 searos or that he is only a gadol once he turns 13?

When I read the gemara/Rashi, I understood it to mean that it turns out he was a gadol l'maphrea - from the time the searos grew as long as the searos are still there when he turns 13 so we can be sure that it wasn't just shuma. However, R' Tendler corrected me and sure enough someone with the Artscroll said that the footnote on the bottom quoted the Ritva and others who learn that he's only a gadol once he turns 13. I looked up the Ritva in the Mossad Harav Kook edition and the footnote on the bottom says that it's actually a machlokes amoraim in the Yerushalmi about whether it works l'maphrea or not. It's also a machlokes Rishonim - he quotes the Rosh who argues with the Ritva and holds it is l'maphrea.