What is the ideal room size for the old MBL 101

Is 23 sqm too small

Amps - MBL 9010C
Pre Amps - MBL Programm 1992
IMO, you're probably right at the margin.

This speaker generates a lot of bass and is -to my ear- voiced to sound best in a very large space. Your room is somewhat smaller than you'd prefer, so you might well have to do some work (room treatments) to tame the bottom 3 octaves. OTOH, people have certainly stuffed them into smaller spaces than yours.

Good Luck