You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Nikola_Tesla

Context:
On 30 July 1891, at the age of 35, Tesla became a naturalized citizen of the United States, and established his South Fifth Avenue laboratory, and later another at 46 E. Houston Street, in New York. He lit electric lamps wirelessly at both locations, demonstrating the potential of wireless power transmission. In the same year, he patented the Tesla coil.

Question:
How old was Tesla when he became a citizen of the US?

35