Well, the short answer is that it is never too late and sometimes doing it right now is better than leaving the job until later, as branches can become woodier and thicker making the job significantly harder.
In general, with citrus, pruning them a little bit over the entire year, except when full of fruit, is best. If there are branches you want to remove that have fruit on them, wait until you have harvested the fruit before cutting off the branch.
Lightly prune areas that have become a little full and congested or where there has been a spurt of growth upward, as too much energy in that direction means it is not being given to more productive areas.
Anything growing out more than 10 - 15 cm from where you want the tree to be, can be cut off – unless of course there are flowers or fruit on it. Remove long weeping branches that are not producing and remove overlapping branches.
If you like, why not try to turn an offcut into a new tree, even if it does not work, it will give you some experience in how to do that. Cut a length to about 30cms, remove the top and bottom leaves, leaving say 4 or so in the middle, gently tap the base to open up the stem and plant it, maybe in a pot to get it going, or try it straight into the ground. Feed and water and keep an eye on it. Then see what happens. It's just another part of gardening’s trials and errors, learning and growing, and who knows, you may make another tree, which is a pretty special thing to have done.
Enjoy
Peter