The passive voice construction is strange, clumsy and unnecessary. The first sentence is already performing something similar to passive because the subject (the people who know about the elderly gentleman) is not stated.

The first sentence states that it is worthwhile to gain knowledge about the gentleman. Is that what you intend to say? It does not state that it is worthwhile to become acquainted with the gentleman. I don't understand the second sentence at all.

Well, I suggest that both sentences you wrote convey the same meaning in a natural way, while the sole distinction is that "worth knowing about" utilizes an active voice to express a passive sense. In my opinion, the first appears to be much more prevalent and acceptable. Another homogenous instance is just like yours : (1) It might be worth calling her. (2) Beyond those ten minutes there did not seem, just then, to be anything worth being called Time. [ Reference: << To the lighthouse>> - Virginia Wolf, Chapter 36. ] For the reason that someone refers to the usage of "worth + being done" as grammatically incorrect. Therefore, I have provided an authoritative example to substantiate its validity here : D