No, the coins will eventually stake. coin-age is a weight. The more time passes, the more weight it gains (You can check coin control to see this in action). Before 10 days, the coin-age is not enough for the block to have permission to stake. After 10 days, the coin-age still grows but now it satisfies the minimum weight to have a chance to compete for the stake. The coin-age will grow until day 30, after 30 days, the weight is MAXED out for that specific block. So in other words, the coin-age won't grow anymore.
So to answer your question, the coins will stake, but since it's a matter of competition, there is a bit of luck for when you will actually see the stake happen.
The smaller the block, the longer it will usually take since the coin-age is (and I don't remember the exact formula) based on block size * time.