jobo
Grandmaster
Constant mean all the time, all day everyday, you need to be fitter at 6 than you were at 5 which is fitter than you were at 4. And then day after day,That depends what we consider "consistent". If we say gains every day, not gonna be consistent. If we say gains every month, with a decreasing curve, that's going to be a consistent trend until they either get injured, reach their current max at the current training level, or some such.
We can also say it won't be "every person will gain by the same curve", but we can say that every non-runner with the ability to improve will improve their running ability (consistently across the population) by practicing running.