Unless you've hit a home run with one of your startups (which, incidentally, eliminates the need to worry about money again), you'd better start that VC transition before you turn 50.
Starting any major career change after 50 is dicey. I'm not sure there's anything special about VC in this regard.
Harry Bernstein began writing his first novel at 93. He published it and gained fame at 96. He published two more before he turned 101. His fourth book will be published this year (posthumously, unfortunately).
Is 50 too late to start a new career? Only if we decide so in our minds.
Starting any major career change after 50 is dicey. I'm not sure there's anything special about VC in this regard.