Hello,

conventionally, the age of the student at the first year of their btech would be 18 years and the age would be 22 years when they are graduated. So looking at your bother's age, it's not a big problem it's just a year difference. However, ask him to not worry about the age. What everything matters at the end how capable he is to get hired in any company. If he's pursuing computer science then he must be proficient in programming languages and scripting language, databases.  He must be good at coding. All these skills are enough to crack the interview. And one more important thing is his communication skills. So focus on acquiring these skills rather than worrying about age.