There is (almost) no limit to how often a user can answer questions.
If this user is posting lots of good answers, maybe because he is new to the site and finds all this fun, then great! The more the merrier.
However if these are low quality, then there is a problem. Low quality posts, no matter the frequency, are an issue and should be dealt with. SE has many different ways to handle them: CV, DV, edit, flag, delete.
Guidelines for reviewing low-quality posts
I have not seen anything out of the ordinary, (when a user is new they are likely to #1 be quite active, and #2 their posts will not be the highest quality.) Add that together and you get more then "normal" about of answers.
Hopefully the user(s) you are referring to will quickly learn that it is much more beneficial to write a few excellent answers, then it is to flood as many answers as you can while having none of them really stand out.
You can help speed up that learning process by commenting on any answer and ask for more info, (DV and comment if it is really not good), if it is really bad flag it as "very low quality."
But you could do the same things that I would do after getting a flag. Give the user some links, links to the SE good answer help page, other good answers, etc. Leave the user a comment inviting him to chat to learn more.
Finally don't reward mediocrity, if the answer doesn't deserve a DV, but is not particularity great, then don't UV it. It doesn't take long when getting little to no rep on an answer to wonder what is wrong with it.