This was such an interesting question that I reached out to the law firm that advertises on this site (rgbavocats.com). They answered the following:
1. With regard to adults, applicants who wish to nationalize must have at least (02) years of legal residence; according to Article 3°, sub-section 1) of Law N° 26574 - Law of Peruvian Nationality (hereinafter the "Law"). It should be noted here that applicants must submit their application according to their current migratory category.
2. In regard to minors, they can apply for legal residence under the category of Relative of a Peruvian Resident (Familiar Residente), however they cannot apply for Peruvian citizenship until they reach the age of eighteen (18); according to Article 4° of the Law.
3. With regards to the loss of foreign nationality, the Peruvian National Superintendence of Immigration does not explicitly ask applicants to renounce their foreign nationality before the appropriate entities, so nationalized Peruvian citizens may retain their foreign citizenship.
I hope this helps