Had me guessing as to how much younger. 5 years? 27-29 was a very long time ago here. I guess if I'd been interested in track 200s etc, it might have been still possible in the early 50s given past experience. I'd have to find some age-group averages for a better sense.
How about 30 years younger! My "fast friends" are post collegiate mid 20s who run 22s for the 200 and 45-46 for the 400. Next Oldest is a late 30s transplant from Boston (Law Prof at the U) and he was running 30-32s for the reps mentioned which were intended to be run at 80% effort with (for sprinters) relatively short recovery. Otherwise they would target 24-26 for a speed session. Thanks to Coach Anton's prescriptions I've got a better appreciation of sprint training.
BTW it's really instructive to watch (from behind at least!) the fluidity these elite type sprinters have and how they get speed over ground from a combination of power take off, which drives stride length, and high leg turnover cadence.
Anyhow for reference top M60's run 27sec under race conditions indoors and I'm 1-2 secs off that. And yes for early 50s those times very doable as you suggest. Mind you to do those without injury requires some specific conditioning.
Nothing like youth to be fluid & fast - it seems to start well under ten when one notes the ways most kids under 10 fly around. And so by the time 15-6 rolls around, well.... Without going to look, 45-6, for say Big 10 collegiate 400, must be about average good.
Re collegiate 400s, certainly for outdoors 45-46. Indoors 48s seem to be par.