Back to the point - beef and dairy producers need to make a profit. It has been long proven that you need to get a BOVINE into production as soon as possible - that has been setting a goal for calving at 24 months. Saving money by feeding less/lower quality feed to raise heifers has been proven to COST MORE than feeding lots of good quality feed & growing them out properly to calve at 24 months old. There is some research now on calving at 20 months - but I believe they are calving oK but having trouble on next gestation.
Calves that are not growing adequately (proper size to breed at same age as contemporaries) is a cull - period. Cannot afford to keep those genetics - sold as a feeder - not a breeder. Well, I say period - there are ALWAYS extenuating circumstances - as a small breeder, you can fudge - like set of twin heifers raised on own dam. Can keep over for fall calving instead of spring.