Girls, younger sister is dating much older man, should I intervene or not?

My younger sister is 20 and got a job as a café waitress. I recently found out she's going on a date with a regular customer a 42 y/o man.

1) Should I be concerned with that age gap? Is it normal or fishy?
2) As her elder brother, is it acceptable for me to intervene or not? Is that within the bounds of acceptability? Should I totally stay out of it?

What should I do (if anything)
Girls, younger sister is dating much older man, should I intervene or not?
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