Translation:She has been writing books since she was fourteen.
First I translated this sentence in my head as "She has been writing books since her fourteenth year", before I realized that črnácti is cardinal, not ordinal. This is strange to me, and led me to wonder if the sentence could be written with ordinal number form instead. Would the following sentence be understood and carry the same meaning as the origin sentence for this discussion tread? "Knihy píše od své čtrnáctého roku"
"Od svého čtrnáctého roku" is almost always in first-person, sometimes female as "said person's" does not change with gender, and automatically translated as "since I was fourteen" but technically in English during one's fourteenth year one is thirteen years old, freshly a teenager. At the end of one's fourteenth year since birth one is counted fourteen (full) years-old, much like telling time in Czech . . .
"od čtrnáctého roku" 284 hits
"od čtrnácti roků" 109
"od svého čtrnáctého roku" 101
"od svých čtrnácti roků" 7
So what exactly is going on there?
Do not use Google as a language corpus. The numbers reported at the first page of the results is often completely unreliable. Also, evaluating the examples requires some practice or language proficiency.
There is one similar example in the Czech national corpus ", s nimiž se stýkala od svého čtrnáctého roku ". So it can be seen here and there, but 560 "od svých čtrnácti let" and 1,745 "od čtrnácti let".