Given that the Hunter exam is once a year and Tonpa currently holds the record for most continuous attempts. We can tell for certain the the person with the most attempts is at least 50 years old given that they took their first exam at 10 and didn't make any continuous attempts over 6-29.

Someone who knows about the hunter exam and isn't passing isn't uncommon. However it is uncommon for Tonpa to not recognize anyone from previous years. So who could have entered 35 times and never met Tonpa? Tonpas dad of course. Tonpa is on the same journey Gon is, except, Tonpas dad is stated to be one of the top 5 best exam takers in the world. He eventually passed and obviously wasn't allowed to re-enter so he did the next best thing.