Pages (3.6.2) and most of the versions after that are limited to 999 rows in a table.
If you need more, your choices are to add a new table, or to move your table (via copy and paste) to a Numbers document where a single table can have 16000 rows (rounded down to the nearest thousamd).
Numbers did get a slight boost in the current version (10.x) to a maximum 1,000,000 rows in each table. Pages 10 may have had it's maximum increased as well.
Regards,
Barry
PS: A quicker way to add rows to a table (in Numbers or Pages) is to select a group of cells in as many rows as you want to add, then press option-down arrow to add that many rows below the last one containing one of the selected cells. Using the up arrow will add rows above the selected rows, using the left or right arrows will add columns to left or right of the selected group.
B.