On the one hand, some of them look like they could be very young fish of around 2" in size, and approx. 2+ months old. But that's definitely not the case, since you've had them for 5 months yourself, and who knows how long the previous owner had them before you got them.
(Do you know if the former owner bred them himself ? And were the fish approx. the same size as they are now when you got them 5 months ago ? Are they around 2" -2.5" ?)
In any event, they are quite obviously stunted fish at that age. The fish in the lower right corner of photo # 3 is a good example of this. And you can readily see the poor football-shape of fish in photo # 5.
Well & properly raised and cared for discus of 6 months or more of age (as yours no doubt are) should have a good coloration by now, approaching their adult coloration (which yours do not), and should be around 4"or more, up to 5" in size, at that point.
The good news is that you appear to be looking after them well enough - they seem alert and reasonably healthy - and while the likelihood of their growing out to any respectable size is very slim indeed, you can nonetheless continue to care well for them and take pleasure from them over time.
Best of luck to you.
Should you wish to further your discus hobby at any time, I would suggest you obtain known good quality, well-shaped discus, from an experienced, reliable, and reputable supply source, whether that be a breeder or importer of quality discus.