Here is a link to the explanation of terms and conditions. Your points expiration question is in item #8.
Hope this helps.
Although there is an official policy of expiration after 24 months, I dont believe they have ever invoked the rule. I havent earned poins for several years, but happily spent some on a hotel night last weekend, and it was a doddle to do! Unliike my Hilton or Aer Lingus points, which disappeared without trace after a year!