A couple more things are worth saying in relation to this post about Welsh.
First, someone asked me if the story of Welsh over the twentieth century had been a story of steady decline, which I seem to have implied. That may be misleading. The overall pattern has certainly been decline, but things are now rather stable: there remain lots of communities throughout Wales where Welsh is the first language (and quite a few where people’s everyday language is constituted by a mixture of Welsh and English) and we can assume that these will probably continue to exist in coming generations. There is also, apparently, a growth in numbers of Welsh-speakers in cities like Cardiff, presumably related to the Assembly.
The second point relates to what I said about the age of Welsh. I talked about Welsh splitting off from the other Indo-European languages. I should be clear about what we’re talking about: first, Welsh belongs to the Celtic group of Indo-European languages, which also includes Cornish, Breton, Irish, Scottish Gaelic, and Manx (and once included Gaulish, among other dead languages). When this group split off from the other Indo-European subgroups is rather unclear; there is some evidence that the Celtic and Italic languages (including Latin and its descendants) might have split off together before separating from each other (which would make Welsh and Italian more closely related than, say, Welsh and English, albeit still distantly). The evidence is very scant, however, and this remains uncertain.
Later, Proto-Celtic split again, and the Celtic languages spoken today are all descended from either Old British (once spoken throughout the area now covered by Wales, England and southern Scotland) or Old Irish (spoken on what is now Ireland, and brought over from Ireland to Scotland and the Isle of Man). By the end of the Roman period, there is some evidence (though it’s also a bit unclear) that Old British could be divided into two broad dialects: one which covered the areas now known as Wales, northern England and southern Scotland, and another that covered what is now southern England. Cornish and Breton are descended from the southern dialect. Welsh is the only modern descendant of the north-western dialect.
So how old is Welsh? Hard to say; it depends on when we decide it starts being Welsh. Imagine if, in the future American English and British English were more or less mutually unintelligible. When would we say the split actually happened? When the first settlers moved to America? When Webster published his first dictionary? We’d probably want to say that the split took place over a number of centuries. It’s like the question of when a few grains of sand becomes a pile. With that in mind, I reckon most scholars would be happy to say that Welsh came into being, as distinct from other Old-British dialects, sometime between the fifth and eighth centuries. This, incidentally, is around the time the Germanic tribes were arriving in Britain, bringing with them the dialects that would come to form English.
So that would make Welsh about as old (or perhaps only slightly older) than English. Though if, as my fiancée suggested, when people say “Welsh is an especially old language”, they mean “Welsh is an especially conservative language”—that is, that it has changed more slowly than other languages, that the modern form of Welsh goes back a long way—then it certainly is a little older than English. But that’s not saying all that much. And you’re still stuck with the problem of deciding how many grains of sand make a pile: Welsh has changed in the last hundred years, just as English has.