Quadratic formula in mixed linear model

[Ada C]

I wonder how to express a quadratic formula in mixed linear model?

If I want to fit a model: Height ~ age + age^2, how should I express age^2 in stats? In R, ploy(age, 2) should work for such model. I've tried ^, ploy() and I() but all of them arise error. ** would not cause an error, but the params does not has the coefficient for the term age^2. I didn't find similar example in document.

Thanks a lot!

[David Shin]

I wonder if this is similar to what you are looking for. 

https://stackoverflow.com/questions/31978948/python-stats-models-quadratic-term-in-regression

[Ada C]

Oh yes, it works. Thanks very much.