opalo:Yes, it follows the Fundamento, and the Academy recommends it, but there is room for disagreement, and my old dictionary gives the months with small letters. Generally you capitalize names of people and places, when they are nouns, and not much else.

Writing the nominal form of months with a minuscule would however directly contradict the Fundamento, in this case the Ekzercaro:

Fundamenta Ekzercaro: Georgo Vaŝington estis naskita la dudek duan de Februaro de la jaro mil sepcent tridek dua.

Take a look too at the Universala Vortaro, which is also part of the Fundamento:

Universala Vortaro:nov' nouveau | new | neu | новый | nowy.
Novembr' Novembre | November | November | Ноябрь | Listopad.
novic' novice | novice | Noviz | послушникъ | nowicyusz.

The problem is that the Fundamento is inconsistent: it says franco in the text and then gives Franco in the Vortaro, and then polo in both the text and the Vortaro; in the quoted section it incorrectly capitalizes the French novembre and the Polish listopad; and so on. And yet Zamenhof inspected this text carefully. For this reason, grammarians do not try to specify Fundamenta capitalization, relegating the matter to best practices and typography, and the Academy calls it a non-issue.