Translation:Young adults do not often read the newspaper.
Exactly..."Often" at the end of the sentence needs to be accepted...it just depends on where you wish to place the emphasis...They don't read the newspaper often, they only read it once every few months. Or they don't often read the newspaper, because they prefer novels. Reported 27/10/2018.
I think you need to say the young adults. "The young adults" means a particular set of adults whereas "young adults" means all young adults, which is not the case. In English, to convey the correct message it would be "some young adults" that is not all nor a specific group. The placement of "often" is an issue in this question too. The answer at the top of the page is probably the correct answer in a strictly grammatical sence, but in English conversation you would mainly hear it spoken as you have placed it.
There must be thousands of reports (I'm assuming you use the report button feature) that DuoLingo receives each day. Over the years, I've submitted several "my response should have been accepted". Months afterwards I'll receive a note that they have made my response one of the accepted alternatives. Clearly they have a review process and it just takes time.
Because the statement is about young adults generally, we commonly don't say "The young adults" but rather "Young adults...". Not that the alternative is incorrect, but it does sound archaic, unless a prior statement required distinguishing young adults from some other group. Similarly, we translate "Le savoir est important" as "Knowledge is important", not "The knowledge is important" unless we are trying to distinguish knoweldge from something else that was claimed as important.
As in the examples I cited above, because the article is required by the grammar, it seems unlikely to be meaningful. The sentence must rely on context to signal whether 'les jeunes' is meant more generally (as seems likely here, because there is no previous reference to a specific group). If the point is to emphasize a particular group of young adults, one would expect something like "Ces jeunes adultes..". (Would welcome a native speaker's take on this.)
"Pas souvent" can directly transate to "not often". I don't think you need to change the word order in English.
We would not place "souvent" at the end but we could do it with "fréquemment" or "très souvent". The length (nber of syllables) of some adverbs may allow for an alternative placement. In this case, you need 3 syllables minimum to place the frequency adverb at the end.