This graduate thesis deals with the analysis of the age effect on second language acquisition. Research shows that there is an age effect on second language acquisition (Singleton, 2004; Nikolov, 2009). The first part of this thesis includes theoretical overview of concepts closely related to second language acquisition, as well as a review of previous research. The aim of the research part of thesis is to examine whether there is a difference in second language acquisition in relation to the beginning of learning a second language. The research was conducted on a sample of 34 students in the Republic of Croatia who attended courses in English during their studies. The initial hypothesis is that age affects second language acquisition, viz. it is assumed that the earlier start of learning a second language means the possibility of achieving higher levels of language competence. A self-assessment questionnaire compiled for the needs of the research and a standardized B2 level knowledge test according to CEFR, obtained results that indicate that age is one of the factors for second language acquisition.