Yes, I agree that young people should start on helping in their own families first, then their own local community, before they go abroad. They should also learn the language, culture, literature, and history of that country before they go.
When in college, I went on a 'missions trip' with [well-known college Christian fellowship]-- it was a wonderful trip, but not really missions. The local people had no idea who we were or what we were coming to do or what our skills might be. They hoped for mature missionaries who could inspire their churches and bring in a lot of new people, whom they would disciple once we were gone. But we were just young & shy students who hardly could speak the language.
It was a very valuable experience, nonetheless, but it was a 'cross-cultural Christian experience,' not a 'missions trip.' We learned all the things that PPs have noted above.
I have a dear friend who is a priest in Africa. He emphasized to us that the churches there need to mature and be able to support themselves without relying on handouts. Is it possible that missions trips are keeping the churches from that? Or, are they helping the local churches mature? We Americans need to think about this.