Is that normal, The plant grew really fast until it started to grow from its old leaves.
Now the growth is kinda slower.
Is that normal?

Those are new stems coming up. Your plant looks healthy, it may want a bit brighter light if it is growing too quickly or stretching toward the window.

Check out the links below.

http://gardeningsolutions.ifas...

http://www.aroid.org/aroidf/vi...