it is, but it is not "mission impossible" :) it depends a lot on how much time you can spend on each language, how similar or different they are, what is your level, whether you have possibility to practice it with native speakers/teacher, how fast you want to learn and finally whether you are motivated enough to learn these languages. I use English and Hungarian every day, speak Russian when i have possibility, watch TV in German and attend Polish classes so can say have some experience in studying few languages at the same time. I do think there is a limit though. I strongly believe it is not possible to learn more than 3 languages intensively at the same time. But maybe if you are very very motivated, you can do better than that :) whatever the case is, good luck!

Even though it is not advisable, you can definitely learn multiple languages at the same time given that you can manage to have more time for this and you are not thinking or worrying about anything else. One more thing to consider is the availability of those persons who will help you regarding this.

No ,I don`t think so.If we have motivation it will be very easy to learn them at the same time :)

As you age, your memory will too. If you are young, your memory is at it's peak, so it will be easier to learn and easier to forget as you age. I suggest you only learn three languages at most :)

I think it will be difficult! Try to learn one language, because if you learn more than one, may be you mix between it and the other language you are learning.