The classic way to address this is to just ignore the scientific and moral ramifications and complications of actual cloning. What happens is you get the egg and sperm and put it into a giant test tube that provides it with all the necessary nutrients to grow. If that bothers you, than you can upgrade it to a fetus, which is removed from a surrogate mother or a newborn child who is removed via c-section and placed in the tube. Either way, you get a baby into a giant test tube.
The test tube is designed to accelerate the growth, the actual speed is up to you. You can make it take decades, years, months, days or minutes. In Altered Carbon, the main character is able to create a clone of himself in what feels like a few minutes, this could be some advance 3D printing or a very fast accelerated cloning process. You could also have blank human clones, which you merge with DNA and then they will form the shape of the hosts DNA. Its also show in futurama with a more classical test tube approach. As for actual growth methods, it could be chemical induced, via sonic ways which improve growth or maybe you have a localized time machine.
Once you have a full sized adult you going to need to give it some memories. No one needs a full grown adult who can't talk, walk and shits themselves at will. You can map out the hosts brain waves and transplant them into the clones mind, effectively duplicating the host, maybe you can imprint the memories, by forcing them to watch videos and descriptions of all their exploits and daily life.
The biggest issue with any fast cloning, is your going to need to make it expensive, or rare enough so that no one else thinks of using it, or can use it. It could be restricted technology, extremely expensive, banned and punishable by death.
Another suggestion would be to have a duplicate, sort of the same as the Mission Impossible style, with a full face mask and voice changer. If your even more dedicated, you could apply corrective surgery to ensure their body is the same shape as the host. The duplicate person would simply need to memorize any life or large achievements and history of the host to be able to roughly duplicate their behavior and actions. This would be possible with today technology I believe. While the mask in Mission Impossible are a bit rough, there are professionals who can make you real life masks to be able to perfectly imitate another person.