You don't say how old you are, but you're never too young or too old to start. Of course, your goals might be different depending on what age you start at, but learning to partner dance is an enjoyable activity and is a useful skill to have throughout one's life. The people who are the top competitors started when they were as young as 8 years old. Some of the best amateur dancers in the US are just barely out of their teens.
Even if your goal is just to have fun going to social dance parties and being able to enjoy dancing with anyone and having a good time, you're not too young to start. Most of these parties are held at dance studios where they don't serve alcohol, so if you're under-21 you will still be able to get in.
You start by finding a place to take lessons. Try clicking on "Dance Directory" on the left of this web page to search for studios in your area. Or tell us where you live and perhaps someone reading this thread can make a direct recommendation.