First of all, be patient, and let’s clarify some THINGS. This will help us to understand why there are so many categories, names, or branches about Chinese characters ONLINE(or on Quora), making it seems like to understand Chinese characters is much more complicated than to achieve controlled nuclear fusion in engineering.
#1. All the Chinese characters you can see now, whether it is online, on telly, in store signs, or books, they are all the same Chinese characters. There are absolutely not any thing like “Northern ones/Southern ones/Beijing ones/Shanghai ones, etc.” since the Han dynasty. All the Chinese characters share the same origin which would be “continuously created by the Chinese people over thousands of years through their daily activities”, meaning that Chinese people have been constantly creating Chinese characters, even in nowadays.
Take a look at the quantity of characters collected in dictionaries from different eras:
So, let’s remember this: Chinese characters were not delivered by some kind of SpaceX rocket from Mars in ancient times and just happened to land in China, where the Chinese then started using them.
Well, since Chinese people have been creating characters for thousands of years, at what times did they create which characters? Is there a chart that lists the birthdates of all Chinese characters?
Can’t tell. Maybe we could take a time machine back thousands of years, make such a chart, and when we return with this chart, the Nobel Super Awesome Award will be ours.
#2. There have been different printed and handwritten forms for same Chinese characters, especially since the Song dynasty. There is a significant difference between printed and handwritten forms, and the variations among handwritten styles from different guys or different eras are even greater. Make sure you will not be driven crazy by them.
As you can see, a character can be written in different forms, but in fact, they are the same character. Unfortunately, before the Tang Dynasty, almost all Chinese books were handwritten. So, we can boldly speculate, could many characters actually be the same one? This is the third thing we need to clarify.
#3. There are too many Chinese characters that are identical in pronunciation, meaning, and usage, but have different forms in strokes. They are identified as one same character, and these ones have been creating throughout thousands of years of history. We may call them the variants. And a significant portion of these variant characters arose because handwritten forms varied too much or just were written incorrectly at ancient times. After being passed down for decades, they eventually became recognized as different characters. As a result, throughout thousands of years of history, many variants were created in this way.
Based on the THINGS #1, #2, #3 we clarified, let’s do the math. Assuming that each of the 50000 characters we currently have includes one variant, we would actually only have 25,000 real Chinese characters, don’t we?
Therefore, after graduating from middle school, Chinese folks only learns about 3,000 characters, and these 3,000 characters are definitely enough for the daily life, even though there are currently about 50,000 characters recorded. Aside from some uncommon characters used in ancient literature, many of them are variants.
Now, When was simplified Chinese characters created?
Straight to the point, the entire history of Chinese characters is an endless cycle of creation, standardization, modification, and variation followed by more creation. Simplified characters are also a part of this cycle and no different from traditional ones.
Based on the archaeological discoveries, shall we say “They were created 2000 years ago”.
Or,
Based on this book, shall we say “They were created 500 years ago”.
Or,
Based on the periodic table of elements, shall we say “They were created in the year of 2017”.
Thus, if your question is when simplified characters were officially recognized, or when simplified and traditional characters were officially recognized, the answer is quite simple, and it would be in the 1950s. However, not an answer might fit your question now, if must have one, it should only be, at any time.