That’s a tough question!
We could do it now, we can definitely get people to Mars. The problem is they wouldn’t survive for very long. The main problems we face are lack of oxygen, food, water, and too much radiation. If we can find a way to recycle and clean lots of water and make breathable air, that will solve the main problems. We can grow food on mars if we’re clever and we can shelter ourselves with special lead houses.
This technology is very far in the future though. I think it could be manageable in the next 100 – 150 years. But we won’t be using that tech on Mars, we’ll be using it to save Earth first!