I was gaming with a friend at his house, and his grandfather told me this phrase which I don't understand.
The friend explained that 少壮不努力 means I don't study hard when I'm young, and he explained that 老大徒伤悲 means that a gang leader would be sad about me.
Obviously I know he's joking about 老大 being a gang leader, but he didn't want to tell me the real meaning, and I couldn't find what 老大 officially means. According to Wikipedia, 老大 could mean
The honorific title to the elder brother .
Respect for the boss .
Respect for the leader .
The name for the gang leader.
Respectful title for chiefs and superiors .
The honorific title for "older people".
Common name for "the number one person".
What is the correct meaning for this context?