ПРавильно ли я построила предложения? Если не. Напишите правильно. И где мои…

1) At that time, when I'm 25, people will have a good education2) By the time when I will be 25, the Earth will be contaminated3) While we do not pollute the planet, our people will not have problems. Первое- While the people in our cities will not litter, they will not do harm the planet. Второе- While the people in our cities, they have to worry about the cleanliness of the city and the planet.Until very dirty should not walk, so we will take care of the planet and the city to monitor the purity Я думаю, что, нужно так)