stellar evolution - How is the age of a star on the Henyey track calculated?

I was reading Stellar Evolution in Early Phases of Gravitational Contraction, by Chushiro Henyey, where he writes,

If $L propto R^{-alpha}$ along the path, the age of a star from the time when $R=infty$ is given by

$$t=C/(1-alpha), C=GM^2/RL=10^{7.20}left(frac{M}{M_{odot}}right)^2frac{R_{odot}}{R}frac{L_{odot}}{L}text{ years}$$
where $R$ and $L$ are the present values.

This seems to be just for stars on the Hayashi track (and treated here just for Population 1 stars). Is there a similar expression for stars on the Henyey track, or is the same expression valid in both scenarios?

• Next earth - How many planets have we discovered that can support human life?
• Previous Is there any hard evidence that rogue planets exist?