A voucher is valid one from the date of issue no matter when is your next trip.

bear in mind that AF only releases fares up to a year so you cannot book now tickets after June 2024 for now.

if you get your voucher this Summer, you have until the same date next year to use it. So let’s say you get it by Aug 15th 2023, it is valid till Aug 15th 2024 and on this date you can book a trip until Aug 2025