We’ve seen it thousands of times. A 14-year-old or younger playing Mom, or even worse: Grandma. I know why it’s done and it’s the same problem I have when picking shows. There just isn’t enough good material that has only (or even primarily) middle school/high school characters. So, the person in charge of picking shows does what 99% of other theatres do, they pick the best storyline they can that their students can handle.
This cheapens the theatre experience for any audience member and keeps the performance from being anything other than alright. A school student doesn’t have the life experience to portray an adult, even if the adult they are asked to play is very basic and stereotypical. Doing so is asking too much of your student and puts them in a no win position. The tendency of any student actor, especially when they’re uncomfortable with the work being performed, is to overact. Allowing them to be put in this position is unfair to them and to the other cast members who share the stage with them.
What are we to do then? The best, and only option is to have those roles that are written for adults be performed by adults. It will most certainly take extra work on the part of the play selection person. S/he will have to really think about what adults there are to work with. And it will especially be challenging for school drama clubs, where most of the teachers are eager to leave right after the school bell and have no desire to stick around to be part of a drama club production. But in order to elevate your performance to the next level it must be done.
My suggestion: Start reaching out now. Let the adults in your theatre circle know that there may be a chance that you could use their help. Give them time to get their heads around it, and I’m willing to bet that when that time comes you’ll get far more adults saying yes rather than no.