I think that will depend on the country you are working on.
I work in Malaysia, and by that age, you will have hard time finding work as a developer, since people are expecting you to start manage other people after a certain age.
The economics are different, most jobs here are based on projects, there is not much product work. Even if you get infinitely better over time, there is not much economic on leveraging the knowledge, especially if you are the only one on the team that can be that good.
Companies tend not to keep people long and people are keep moving on companies once projects are done, unless new projects are on the line.
Since the turnover rate is high, it will only make sense to keep thing simple, hence there is not much use of much advanced knowledge of anyone.
Because of that, up to a certain age, you very much reached the plateau of the max knowledge expected at the market. Keeping your development skill better may help you with your job, but it may not bring much to the negotiation table. That also means, it make sense to hire cheaper, younger talent if both have reach past the plateau, no matter which one is better. I am guessing this is a reason that people are expecting you to move "up" to the management ladder past the age.