An issue was discovered in the v3.0 wallet which affected staking - sadly, despite testing prior to release, this issue crept in, hence the need to release v3.1 of the wallet. Your coins' age will be maintained, and the v3.1 blockchain comes into effect at block 950,000 (in about a day's time) - at that point, your coins will be mature enough to stake straightaway if they're over 5.6 days old.

It's not an ideal situation, but the dev team got onto it as soon as they possibly could