The external frame backpacks have great weight transfer and airflow ventilation on your back. You can carry more stuff with the side pockets. It is more comfortable even for a short trip or a week-long trip out camping and hiking. It can be adjusted to move the weight around and is made tough. And you can tie more gear to the frame and it has the retro look. Your load can wobble more and be wide, so it could snag easily, if in the brush when hiking. So don't knock it till you have tried it. One pack you will find for youth or young adults is the Alps Red Rock Rust. You might like the Alps Bryce Backpack for a short trip, but if you need to carry more gear. You might consider the Alps Zion with 3900 cubic inches of room.and lower cost, but still have quality.
All prices are in USD.