Yes, cows get stunted. Case in point... We had 2 heifers, that got bred at about 10 months or so while still on the cows... Bulls were put in there late as we were trying to get away from the Jan/Feb calvings to later in March... couple of bought cows, etc, trying to get them in the calving window with ours. Bulls were also not gotten out as soon as they should have been due to some unavoidable things happening. So, they got bred too young... and by the time we realized they were bred, they were too far along to safely abort them. So, they did not continue to grow like they should have if they had been bred at 15-18 months... plus they were carrying a fetus... so all the body's energy went into growing that fetus and not to the heifers. Both calves successfully, and did a fair job raising the calves considering. But they are smaller than their "same age" counterparts, and will never get as big as the rest of that group are and will continue to grow more until they are 3 or 4... We held them over, so did not get bred again until the next group so got a longer dry period after we pulled the calves and got them on feed at about 5 months... and they have done okay with their 2nd calves... BUT.... they are several hundred pounds lighter and smaller in stature. They will never attain the size of the rest of that group. If they were not from a couple of our better cows, they would never have had the 2nd chance.
Bought a group of 11 cows from a friend that had health issues... He did not keep good records... several had 4-500+ lb calves and when we had them preg checked they were needing to be dried up to calve again...(6-7 months preg)... Come to find out 2 of the heifer calves were also bred... and lost one in a very difficult birth, she prolapsed and bled internally... vet said the difficult birth was a BIG contributing factor... and the other had a dead calf after having to pull it and it took some time for her to recover, uterine infection and then did not breed back... So nearly 6 months getting her squared away and then she did not breed. Neither was 850 lbs when they calved...
All that said, your heifers do not look bad considering what you said was their start... but again, they are "old heifers" for the size they are... If you do keep them to breed, please find an easy calving bull so their first calves are SMALL..... to give them a chance to stretch out inside without a monster bull calf trying to pass through a small pelvis area...
As I said, you are going into this with a big strike against them, no fault of theirs... with the "stunted growth"...
