Q. Is it true what some say that you don’t have to recite kaddish on the yortzait more than fifty years?

A. Some Poskim do write that there is a fifty year limit for maintaining a yortzait and reciting kadish. (Yalkut Yosef – kivud Av Va’em 13: 61, Nitei Gavriel – Avelus 2: 77: 22 n. 40, quote Hedras Kodesh (p. 72) in the name of Mahara’Sh of Belz zy”a, Chaye Yitzchak, More Horim in the name of the Divrei Chaim and others).
Nitei Gavriel explains in their name, that after that time the neshama has already found its tikun (mending and correction) and has reached its correct most elevated place in Gan Eden. He also quotes that the fifty year period reflects the time frame that the Talmud (Shabbos 89b) considers common and correct for the liability of sins. (See Ben Ish Chai, Behar)
Orchos Rabbeinu (1: p. 305 and ibid.) quotes from the Steipler Gaon zt”l, that: “After about fifty years the soul departs totally from the body, and there is no more benefit in visiting the kever. Occasionally, he adds, Hashem leaves the neshama of a tzadik longer, so there will be someone left to pray for them in troubled times. Alternatively, the tzadik himself, may desire to stay longer.”
However, Remoh (Y.D. 376: 4) and Maharil rule that for parents, kadish on the day of yortzait is recited forever. Rav Poalim (4: 17) mentions in the Arizal’s name, that some neshomos even after a millennium may still be reaching for their proper, most sublime and exalted place that corresponds to them, so they would greatly benefit from the good deeds of their children. Minchas Elozor (4: 33) adds that one should not even mention the fifty year limit, since it may be part of the chukos hagoyim and carry Gentile roots.
Orchos Rabbenu (1: p.310, see above) mentions that the Steipler Gaon zt’l recited kadish and davened for his parents even after fifty years. Yalkut Yosef, Nitei Gavriel (ibid.) and others also mention that most Poskim rule to maintain the Yortzait and kadish for parents even after fifty years.
Horav Shlomo Miller’s Shlit’a opinion is that for other relatives that one has honoured them with kadish on the day of their yortzait, such as grandparents, one does not have to continue doing so after fifty years. However, for parents due to the inherent mitzva of kivud Av Va’em that applies even after their demise, one should continue honouring them even after fifty years.
The Rov added, that for other relatives, if one stops reciting kadish after that period, there is no need to be matir neder (annulment of vows), as one can rely on the hataras nedarim declaration said before Rosh Hashana.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a