Max Stake Age: 30 days
whats does it mean?
after 30 days no staking reward?
I think it means it stops staking, all you have to do is change address and let it mature again to stake again.
No, it means, your coins coins don't add more weight after 30 days. When they hit a stake, the chunk that got the block starts again from zero weight and builds it up, until the next hit, max for 30 days.