The reading for this one is a pain. 若 is the same as what you learned with the kanji (わか), but 者 is もの, which isn't what you learned. Think of this: A young person does what they want. They don't follow tradition or do anything the way you'd want them to, just like the reading of this word. Also, their actions make you really want to moan (もの) because ugh, young people. Get off my lawn.
That young person was observing cicadas very closely in the park.
Apparently that young person's money is involved in this matter.
This young man is terrific. You should get his autograph before he becomes a big-shot.