I need more clarity. If you are on the main page of this very forum, as of a few seconds ago, there are 142 pages listed at the bottom, with 1 through 5 showing, with the elipsis [. . .], followed by 142.
If I keep hitting the Next button that's to the right of 142, I move from page 1 to 2, and so on, and flow into pages 6 and later with no issue. If I click on 142, I'm immediately taken to the very end, with posts dating from 2005, with 141, 140, etc. shown to the left.
It is often the case on the more active forums that there can easily be 5 pages of content on any single day, but that won't be the case on the slow ones. You should, however, not be forbidden from transitioning through the totality of the available pages.
Page 5 of this forum shows as its first topic one that dates from February of this year.
If this is not the case for you, the first thing I'd recommend is clearing your browser cache, as browser cache corruption can result in all sorts of inexplicable behavior.