1931 Census of England and Wales, General Report, Table 83 : " Proportion per 1,000 of the Population Aged Three Years and Upwards at Certain Age Groups Returned as able to speak Welsh only and both English and Welsh, Wales and Monmouthshire, 1911, 1921 and 1931".

Ages Welsh only Both English and Welsh
1911 1921 1931 1911 1921 1931
Aged 3 years and upwards 85 63 40 350 308 328
  3 and 4 130 112 96 174 155 125
  5 to 9 97 78 61 265 216 205
  10 to 14 60 47 29 337 275 275
  15 to 24 46 36 20 360 309 315
  25 to 44 62 42 21 378 327 353
  45 to 64 126 83 46 403 366 396
  65 and over 224 166 108 378 353 391