Its difficult to tell what it is from the photo, have you got one of the leaf from the top?, from a photo of the whole leaf you can narrow it down a bit, but it is difficult to be exact, it depends on the size and shape of the leaf, and the petiole size/shape in relation to the leaf

For it to flower depends totaly on what it is and wether its been pruned at all, from when it was planted it keeps count of how many leaves it has grown, and when it gets to the right amount it will start to flower and produce fruit, if you trim bits off the top the leaf count is reduced, so it needs to grow more to age enough to mature, so with all citrus grown from seed its always best not to prune at all

lemon and lime can be fairly quick, sometimes 3 years usualy more like 5 years to flower and fruit, grapefruits can be far slower , more like 15 years

Has it ever flowered?

What plant food do you use?, If its not fertilised and watered correctly it will slow down the growth and can prevent it flowering due to lack of the correct nutrients, too wet can prevent it flowering as well, you are best using a citrus feed in the water when the plant is dry a few inches down, then soaking the plant, they like to be dry then soaked then dry again