In your Settings, you can set how many days in advance you want the customer to be able to book.
For example, you may wish for Table Bookings to only be taken for the next three months.
To set it up:
Click Settings, Sites, then select the venue.
Click Booking Types, then select the relevant booking type.
Scroll down to Restrict advance bookings section and enter the number of days in advance you want to take bookings for.
Click Save.