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!
Western Hindu 
That is absolute rubbish. If it takes more than a lifetime to learn, logically no one will ever know what it is.
Hinduism is a simple religion.
Made complicated by getting intertwined with mythology, social rituals and superstitions.
And is worsened by many Hindus themselves who have made no effort to learn or understand the philosophy and will say anything usually rubbish to hide their ignorance.
One cannot “convert” into Hinduism, for there is no formal process of converting. It is a religious tradition, a way of living, anyone can choose to follow that way. As much or as little.
I agree partially with littleindian: the latter part, but what might just mean a lifetime to learn? In the simplest of simplicities, Hinduism is simple. You are human, and you just plainly ought to do just good. That’s simple yet too difficult to follow for the larger parts of the world today. What will take you more than a lifetime to learn are the details, and in effect, the essence of attaining the higher level will take you more than a lifetime. Not attainable? You would know in the last days of your life that you just completed it only then. It will come to you, provided you tread the right path. So it will take more than a lifetime. Its no joke nor an easy path and has no answers. Its arguable but its not a debate. The answers lie only when you are ready. Sadly, or fortunately, it comes when your destined path shows you the way back ‘home’.
Its a long path, and we ought not be complacent to state that we fully understand. It takes more than a lifetime. You can only make it earlier when you are ready to go. For some at that point, death chooses to stay away.
As RaulRaj wrote, I agree partially with littleindian. It is true some think Hinduism is complex, since it is thousands of years old.
But if you break down every aspect of Hinduism in simple sentences , then Hinduism will be very easy to understand.
For example,
1. For Hindus God, as is, is beyond any attributes of form, color, shapes. Hindus worship only ONE & ONLY God Brahman which expresses itself in trillions of forms.
2. Hindu scriptures state God has no human form or any other form. Man with his very limited thinking ability cannot comprehend a God with out any form. As such Hindu scriptures state there is nothing wrong to start worshiping a God with form even though God is has no form at all. Even in Narada Bhakti Sutra, the greatest devotee of God sage Narada states, “ God I know, you and I are essentially one. Still, I like to keep separate from you to enjoy the magnetic separation.
3. Hindus are not worshiping idols . They are using idols to concentrate one a God who has NO NAME OR FORM.
4. Hindu Salvation is known as SELF REALIZATION. SELF REALIZATION is the way of realizing that one is indeed the immortal soul with in and NOT the perishable MATERIAL body.
5. Hindu scriptures state, salvation or self realization is for all, irrespective of one is a Hindu or not. Any one who searches after truth will finally attain truth. That can happen even to an atheist.
6—Hindu scriptures state that people can attain self realization through one of the four methods. Those four methods are:
A. JANANA YOGA; [path of knowledge]—Hindus have 6 philosophies called Darshanas.
B—KARMA YOGA; [path of unattached, unmotivated actions and thoughts]
C—BHAKTI YOGA; [ path of total surrender of one’s will to God]
D—RAJA YOGA. [path of breathing and Pranayama–eradication of thoughts]