If I was raped 20 years ago by my brother and were to file charges now, would he get in any kind of trouble or would it be a waste of my time?

Regardless of the outcome, if someone is raped they should report the incident and file the charges.  The outcome will turn on a variety of factors-- including the tenacity of the investigors and prosecutors that are eventually assigned to your case.  If you land with less than diligent investigators or prosecutors-- then not much may happen with your case-- right now. 
I emphasize "right now" because many later cases can and do turn on historical reports.  I'm a former prosecutor and can tell you that I frequently looked to see if anyone else had made the same or similar complaint.  I may not have been able to get justice for something that happened 20 years ago... but I was going to make sure that history did not repeat itself.  If for no other reason, than to make a record, your outcry has value.  If your brother is a rapist or pedophile, there has or will be another victim.  In the criminal justice system, it never hurts to have support as a victim-- and victim's supporting victims is an extremely valuable support.  Additionally, the more victims that an investigator sees-- the more stirred up they become to get the case to trial.
The second reason you want to report is similar to the reason above-- to get the incident documented and on file.  The investigating agency may or may not required him to submit to a DNA sample, but more agencies are automatically requiring samples as part of the process of investigation.  If his sample is submitted into one of these databases, then it could return a "hit"-- meaning a link to another unsolved crime where the assailant was not know.  Your reporting may be the key to not only your justice, but the justice for another victim.
Every victim has a reason for not telling sooner.  Many officers understand this.  If it's important for others to know, then you need to tell.  If you need counseling to help you work through some unresolved issues related to the original rape, reporting the incident may also qualify you for victim services to assist with moving forward.
My overall message is that it won't be fun, you won't immediately feel relief, but... reporting the rape can potentially make a huge impact for yourself now... as well as any other victims that are lingering in a similar silence.