Final answer:
The provided information does not reveal the age of Alexander Graham Bell when his brothers died. Instead, it discusses his renowned patent of the telephone during the mid-late 19th century.
Step-by-step explanation:
Alexander Graham Bell is well known for his patent of the telephone issued between 1850 and 1900, which is one of almost 700,000 U.S. patents during that period.
This means that at the time of his brothers' deaths, Alexander Graham Bell would have been in his early twenties, as he was born on March 3, 1847.
For detailed information about his personal life such as the timing of his brothers' deaths, it would be more appropriate to refer to reliable historical records or biographies of Bell.
Learn more about Alexander Graham Bell