**Corrections in blue

**Comments in orange

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Running against darkness

When Marcos was eigthteen he began to participate in mountain races as a blind people guide guide for the blind OR guide for blind people. In a race where people move in complete darkness, the guide role is indispensable. He warns the runner when he finds a hole or a branch on the ground. He can also describe the landscape to make it possible for the runnenrs could to be aware of the things surrounding them ['the things surrounding them' is fine, but 'their surroundings' would sound much better]. Marcos started to lose his sight three years ago,. therefore now Now it is him who needs a guide. It was not easy for him.
Marcos was working as a taxi driver, but now he is not able to drive. He is trying to avoid that his disability sets limits to his life. [This doesn't make sense, but I know what you are trying to say. Perhaps you are trying to say: "He refuses to believe that being disabled will limit his life." OR "He isn't allowing himself to think negatively about his disability."]  He was world champion on in the 2012 Parasky Games. He is on in charge of the "Move for the people who can't" project, which has the aim of to make people to be aware of minority illnesses individuals with disabilties [the word 'minority' doesn't work here] and to encourage disable disabled people to practice sport play sports. On last May, he ran with some friends near nearly a thousands kilometers.

Running Through Darkness

When Marcos was eigthteen, he began to participate in mountain races as a guide for blind people . In a race where people move in complete darkness, the role of the guide is indispensable. He warns the runner when he finds a hole or a branch on the ground. He can also describe the landscape to make it possible for the runnenrs so that they could be aware of the things surrounding them. Marcos started to lose his sight three years ago, therefore now it is him who needs a guide. It was not easy for him.
Marcos was working as a taxi driver, but now he is not able to drive. He is trying to avoid that his disability does limit his life's potential. He was a world champion on 2012 Parasky Games. He is an activist for the "Move for the people who can't " project, which has the goal of making people to be aware of minority illnesses and to encourage disable people to practice sport. On last May, he ran with some friends for nearly a distance of a thousand kilometers.