Is 23 too late to start boxing to become any sort of decent in the boxing game?

Yes, and starting young is hardly any guarantee to be successful either. Don't plan your boxing future based on age, go to the gym and see how good you are/can get before making a plan to capture the green belt.

 

Ron Lyle turned pro at 30. Bonecrusher Smith at 28. Ken Norton was 24. Rocky Marciano was 24. Anthony Mundine was 25. Dwight Qawi was 25. Some of those guys had some amateur experience, some little or none. They all ended up having successful careers.

 

I'm not sure this is true in call cases. Look at Tyson. Even though he wasn't that short he still was short and very effective in the heavy weight division.