Well, sounded reasonable
But after actually looking into the code and since this is from the PACS server module dcmqrdb, I tend for another interpretation
which is also commented in the header file you pointed out:
** Maximum size of things to put in db records.
** Some values will have vm>1 thus these maximums are
** intended to leave enough space for most common uses.
So some fields may be requested with a VM greater than one. Someone back in 1993 or so went through the standard and looked at the maximum VM that could be encountered and that seemed to end up in the values you found, i.e. for Age String there seem to be a maximum of 8 (8*4=32) and for Date a maximum of 10 (10*8 = 80). The latter being not that nice because it will not cope with the old date "dot" format, but that should be very uncommon in a q/r-request anyway.