There is an anecdotal story that someone asked a Hindu about converting to Hinduism. The Hindu replied that Hinduism would take more than a lifetime to learn.
I suspect that this story is just an urban legend, I have certainly never heard any Hindus say such a thing to me. Even so, is this true. If by “learning Hindusim” you mean attaining moksha then the answer is yes. Most Hindus do not expect to reach moksha in this life, so it is hardly a reason not to follow the path of Hinduism.
In any case, only very few people are aware of their previous lives. If someone feels a calling to the path of Hinduism, who can say whether it is a path that they are meant to return to, having followed it in previous lives. Even if someone has not followed Hinduism in previous lives then, to quote a Chinese proverb, “even the longest journey starts with a single step”.
I doubt if anyone ever will tell me that Hinduism will take more than a lifetime to learn, as I said I think it is an “urban legend” rather than something someone said. If anyone does say it to me, I know how I am going to answer!