Peter was 25 when he opened the hotdog stand

[Bassim]

I am wondering if my sentences are grammatically correct.

Peter was 25 when he opened the hotdog stand. When he died about 40 years later, he left behind nine restaurants and four children.

 

[emsr2d2]

I'd probably use "Peter was 25 when he opened his first hotdog stand" to make it clear that that was the start of his career.

 

[Tdol]

If you don't know which hotdog stand the person is talking about, Emsr2d2's version is better. If it's a famous hotdog stand the original could work.