I am fourteen past means I am past fourteen.
From the OED:
past preposition & adverb
1.c. Beyond, older than (a specified age). Also (occasionally) placed after its object.
Source: Oxford English
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These are the attestations there that show the “occasional” usage:
1676 A light gray Gelding..five years old past.
1720 Lost.., a black Mare,..aged three Years past.
1835 This morning my white mare died, being 8 years old past, for which I gave $100 at five years past.
Here is another among them showing past in the more usual position:
1767 His being able, at past eighty, to perform this expedition on foot.
Now, the curious thing is that those occasionals all have to do with horses, and I imagine Helena is not a horse.