I'm regularly asked how many words there are in the mental lexicon. As you all know, much here depends on the definition of person (young/old, reader/non-reader) and the definition of word. Still, it is possible to give reasonable numbers for various definitions.
The short answer is that an English person of 20 years old on average knows 42 thousand lemmas coming from 11,100 word families. A 60-year old knows 6,000 lemmas more.
You can read the detailed answer in this open access article:
Feel free to forward this to other people who may be interested.
All the best,
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