I put a Condy in my tank at three months and it's doing great. Just because it's not reccommended doesn't mean it can't be done. I think it depends on how well you take care of the tank, monitor parameters in the beginning , how well your tank is setup, do you have a skimmer are you using RO/DI , do you have enough good live rock, enough flow, enough light. Chances are new people will not have all of that together in 3months. I didn't, I wasn't using RO/DI, and I didn't have enough flow. But I learned and fixed my issues quickly.
I'd say most local fish stores tanks are probably equivalent to a 3 month old tank. Because while they may have good parameters, they have little to not much bio diversity in the tank, like maybe one piece of rock, not much flow, three nems in the same 20g tank freshly shipped from the other side of the world.
I feel like your Condy will be fine if you half way care about it. Its usually the first thing people notice or ask about in my tank, and it's was one of the cheaper items Ive got.
