Poprawiłem:
Simon Roland was 10 years old when he become hero. One day he was playing on the beach near his home. Simon was building sand castles, when a young man jumped into the water. A few minutes later Simon noticed that the young man was drawning. Simon swam 100 m. and reached the young man who 'unfortunately was unconscious. Simon pulled him back to the beach and phoned for emergency services. The young man recovered a little and thanked Simon for saving his life, then the ambulance took him to the hospital.
Simon Roland was 10 years old when (ale kto? brakuje tego - podwójny podmiot ??) 'was' (niepotr- ok) 'becomming' (zle slowo - zly czas - ok) hero. One day he was playing on the beach near (ale czyjego znajomego? kolezanki? prosze nam to ujawnic - ok)home. Simon was building 'sandy' SAND castles, when A young man 'jump' (tutaj simple past - ok) into the water. A few minutes later Simon noticed THAT THE young man 'who' (po co to? sens:"kilka minut póxniej Simon zauważył młodego człowieka, który tonął") was drawning.
Simon swam 100 m. and reached THE young man who 'unfortunetly' (ortog - ok) was unconscious. Simon pulled him back to the beach and phoned 'to emergency' (ej? chyba FOR emergency services? tu nie wiedziałem bo jest "call the police"). THE young man 'was recovering' (simp,le past- ok) a little and thanked Simon for saving his life, then THE ambulance 'take' (simple past - ok) him to THE hospital.
Chciałbym napisać na końcu coś w stylu. Od tej pory Simon był bardziej odważny i nie bał się pomagać ludziom.