I was 17 when I did Amigos in Paraguay and it was hard.
Outside of urban areas (where all volunteers were in 1992 and I would assume most volunteers still are placed) people speak their local language..it's called guarani and it's unrelated to Spanish. Locals did not speak Spanish that well in my area; we often took a kid with us to translate (guarani to Spanish) when we worked..we were lucky to have a fairly fluent in Spanish, sweet and smart kid around.
It was deeply cool to learn a bit of guarani (the word for milk is camboo..it actually sounds like a cow mooing!) but over all this definitely made it harder. Since people spoke to us in Spanish, we weren't really immersed in either language. And let's be honest.. a big reason people do Amigos is to improve their Spanish. (In our training we had a training day where we named a goal and the first one was "learn some Spanish"..it was followed by audible groans and statements that "she took my goal".) I did improve somewhat in Spanish, but I also cried after spending one day with urban native Spanish speakers and realizing how much more I could have been improving.
I did Amigos again in Costa Rica and I came home very fluent; I still am very fluent. I did major in Spanish in college--so I was much more comfortable in Spanish at age 20 (after 2 years of being a Spanish major in college) than I did been in high school-- but real immersion also made a huge difference.
I have not been back since 1992, so perhaps the country is now a bit more modern. But in the rural areas--or at least my rural area-- there absolutely was nothing around for miles and miles. Besides the social isolation, the remoteness caused real practical problems.
It was hard to be sick! I 17 I had frequent and severe migraines and there was no way to get any medical care. My partner needed medication badly (for an issue she developed there, so she couldn't bring it from home), but my route leader could only come once a week and the week he came he didn't have it. I 100% "get" that locals live that way their whole lives and we are lucky! But that didn't make it easier when both I and my partner were sick and couldn't get what we needed.
At 17 I just didn't think about what would happen if I had a true emergency.. but now at 40 I think of these things :) and it could be very very dangerous to be so isolated if you did break a bone or (heaven forbid) get sexually assaulted.
It was very hard for us to manage our project since so many of our families lived so far from us. We had no personal relationship to the families we helped, nor did they know gringos were in the area with materials for them to make latrines they could use without running water. If families weren't home it was very hard to "just come back later" and some families either could not understand why we were there (obviously this is a language issue as well as a location issue) or were wary of foreigners and would not talk to us. Once we even felt like we were in danger when we were at the door of a hostile family.
Over all I felt we didn't make much of an impact on our community..and now I question why I was even needed there. I think that it would have been more effective to just donate the supplies we had to a local agency and let the agency distribute them rather than placing volunteers in such a remote area to do losa (the cement blocks we had to give out for people to use to build latrines) distribution.
It would be even harder for teens now, because--for better or for worse!-- we are all used to being able to communicate with friends and family via social media and/or skype. (No one had facebook in 1992.) Even I at 40 enjoy posting about my travels on facebook as events happen and if I was traveling without having any facebook access I would miss it. We are also used to being "linked in" to the news now.. Obviously getting away from all of that for a few months has advantages as well, but I think it would be extremely difficult for a north American teen to be in Paraguay for 8 weeks.
I should mention that we did not bond that deeply with our family. They weren't hostile to us (or generally azzholes/hard to be around), but--for whatever reason-- my partners and this family just didn't bond that much. I had two partners and we all three felt jealous when we visited other volunteers who clearly were closer to their families than we were. So perhaps I had bad luck and if you were luckier with your family it would be a much better experience. (But then again..you might not get lucky with your host family just like I didn't.)
I am glad that I went! I learned a lot (about their culture and myself) and hey..where else can you learn guarani and ride around in an ox cart? And I didn't hate it by any means! It was beautiful and peaceful and I still remember the night time stars and the times sitting and drinking mate (the local tea) fondly. Plus it was good to be pushed out of my comfort zone at aged 17--and my transition to college was easier for me since I had done Amigos.
But if you want to go, I think that other countries might be better choices. I should mention a BUT (and a big but!), however. I went in 1992! Now Amigos does focus more on whole community help--rather than just the "pass out the losas..and do dental charlas as a secondary project" mentality they had then; that's great! I am sure that if I had actually been planting trees and helping with garbage pick up--although we were so remote trash everywhere wasn't a major issue-- I would have gotten much more out of Amigos.