To borrow from wikipedia:

The most common form of this fallacy is “A” makes a claim of “fact”, to which “B” asserts that “A” has a personal trait, quality or physical attribute that is repugnant thereby going off-topic, and hence “B” concludes that “A” has their “fact” wrong – without ever addressing the point of the debate.

Questioning someone’s motivations for choosing an argument, their ability to form a sound argument based on their personal experience or the biases they display in an argument is not (generally) an ad hominem. Dismissing you because you have three hands, enjoy anime, support [political party], etc. would be an ad hominem (unless those were the topics being discussed, then maybe it’s not). Saying that your argument is based on a lack of familiarity with the topic being discussed is not. Were this a discussion about the comfort of various shoes, it would be very relevant to disclose that you yourself had lost your feet (heroically saving orphans from a crocodile-filled river).