It sounds like you were away from coding for a really long time (10 years!), then you got back into it, picking an area you didn't know much about, expected it to be easy, maybe didn't put in the time outside of work...this approach wouldn't work for anyone, no matter their age.
Here's a manager-y question for you: how could you have done things differently when you went back to being an IC, to have had a better transition? Maybe doing more prep work before you left the manager track? Maybe going back to C++ instead, or an area that was closer to what you used to work on? Maybe doing open source work in that new java/python target area, to get experience, build a portfolio, and be sure you liked it, before you bet your livelihood and reputation on it?
Here's a manager-y question for you: how could you have done things differently when you went back to being an IC, to have had a better transition? Maybe doing more prep work before you left the manager track? Maybe going back to C++ instead, or an area that was closer to what you used to work on? Maybe doing open source work in that new java/python target area, to get experience, build a portfolio, and be sure you liked it, before you bet your livelihood and reputation on it?