Hello, here’s my correction, in yellow the correct version and in blue some useful comments. Feel free to ask any questions;)

Nowadays more and more people concerned about health.

They go to gum gym to do fitness, yoga, swimming, and other healthy things activities / things good for health.

We live in the time The time we live in is full of too much many machines, manufacture, and pollution environment polluted environment or environment pollution.

So it's very important to care about health.

It's important to eat good food, do exercises and go to a doctor for doing tests and preventing disease see a doctor for a check-up and to prevent any disease.

*** you use twice “important”, it’s correct but you can also use synonyms, so it won’t sound repetitive :) for example: crucial, essential, necessary, imperative… and so on ( it’s just a suggestion)

People should have more rest and don't be nervous.

They are said say, every day walking on in the fresh air to promote helps improving health. 

As for me, I like sports! I'm sporting a sports/ sporty/ athletic girl)))

In summer I am doing stretching, yoga, love walking on in the forest and cycling in summer.

In winter my absolute love is snowboarding.

I was in mounting is call mountains called Yralskie Ural mountains (название гор или мест можно проверять в википедии;)).

I also want to try surfing, it's my dream.