We found 26 dictionaries that define the word mental age:

General (18 matching dictionaries)

1. mental age: Longman Dictionary of Contemporary English
2. mental age: Merriam-Webster
3. mental age: Oxford Learner's Dictionaries
4. mental age: American Heritage Dictionary of the English Language
5. mental age: Collins English Dictionary
6. mental age: Vocabulary.com
7. mental age: Cambridge Advanced Learner's Dictionary
8. mental age: Wiktionary
9. mental age: The Wordsmyth English Dictionary-Thesaurus
10. mental age: Infoplease Dictionary
11. mental age: Dictionary.com
12. Mental age: Wikipedia, the Free Encyclopedia
13. mental age: Rhymezone
14. mental age: FreeDictionary.org
15. mental age: Mnemonic Dictionary
16. mental age: TheFreeDictionary.com

Business (2 matching dictionaries)

17. mental age: Legal dictionary
18. mental age: Financial dictionary

Computing (1 matching dictionary)

19. mental age: Encyclopedia

Medicine (4 matching dictionaries)

20. mental age: Merriam-Webster Medical Dictionary
21. Dorland's Illustrated Medical Dictionary (No longer online)
22. online medical dictionary (No longer online)
23. mental age: Medical dictionary

Miscellaneous (1 matching dictionary)

24. A Brief Critical Dictionary of Education (No longer online)

(Note: See mental_ages as well.)

Definitions from Wiktionary (mental age) ▸ noun:  How old one appears to be based solely on mental ability and function. Similar: emotional age, time of life, head, brainpower, age of reason, age identity, mentalization, childmind, grey matter, mentalisation, more... Opposite: chronological age, physical age ▸ Words similar to mental age ▸ Usage examples for mental age ▸ Idioms related to mental age ▸ Wikipedia articles (New!) ▸ Words that often appear near mental age ▸ Rhymes of mental age ▸ Invented words related to mental age