i looked in performance options,Thread list date limit for performance
Particularly busy or particularly large forums can now set a limit to only display threads that have been updated recently:
This is primarily an option to aid performance. If you have a forum with a large number of threads in it, the standard listing queries will need to look at many of the records to determine if they should be counted. By restricting this to displaying only recent threads by default, fewer records need to be considered.
This option only applies when sorting by the default (last message date). If the sort direction is changed, the limitation will be removed. Further, when a visitor reaches the last page, they will be given the option to display older threads should it be required: