Typecasting is the state where an actor is constantly brought in to act for a particular type of character. It happens across all forms of acting and voice acting is no exception. Some people will be grateful that their voice serves a selected character but others will be rather miffed at the idea of only being able to voice one or two types of characters throughout their careers.
Honestly? I don’t blame them.
Part of the appeal of voice acting (in my opinion) is the idea of being able to voice a wide variety of different characters in different stories across different mediums such as games and animation. To suddenly realize that you might only fit a select few types closes many doors you thought were previously open. Not a good feeling at all.
So what can you do?
The best advice is, of course, practice! Not just practice your regular routine practice voicing things you’ve never voiced before! Take characters from shows you’re watching and record over their lines, try and figure out what makes the character really them. Pick up on techniques other voice actors are using and add those to your repertoire.
But there’s a hard aspect about attempting to break out of a typecast.
If your voice doesn’t commonly fit for the character you’re going for, you’re going to have a much harder time competing for roles than someone whose voice does fit. Is it impossible? Of course not, and don’t let anyone stop you from going for it! But you do need to think about this before submitting that audition.
But if people like your work with a particular type, is it really all that bad?
Personally I think it’s subjective. Someone who constantly voices a young main protagonist may have a much better opinion of their typecast than someone who only voices side characters and the like. But if you enjoy the character you’re voicing then just embrace it and take comfort in the fact that you can probably play that character better than anyone!