Topic: Multiclass characters

In the 90's i could advance my ranger druid monk to high levels or what we called mid level characters back then. With the 5th edition can i have a similar multiclass character who is 10th level in each class? Is there really a restriction to have just 20 class levels? The joy i had in playing my character when he reached 10th level druid and 9th level in ranger and monk classes was high. Why all the chat about medication?