I don't know how much older this guy is but you need to remember, as what Nebula said, people perceive success differently.
What might have been successful 50 years ago, something like a part-time job earns more nowadays. Times are changing and people see success in different things based on what era they grew up in.
If you're working hard to get good grades in school you only need to continue that attitude to get good grades in college/university or whatever you plan on doing in the future.
Not everyone is as "intelligent" as the next person, but everyone has the ability to work hard in whatever it is they're doing and no one should be able to put you down for that.