I see this structure a lot:
What does the 一〇 mean and how do I pronounce it? Is it いちまる?
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Sometimes you find 〇 being used together with kanji numerals (一, 二, 三, ...) to signify "zero".
In horizontal writing it is more common to express numbers using Arabic numerals (0, 1, 2, 3, ...) — and Arabic numerals are often also used in vertical writing.
一〇年以上 = 十年以上 = 10年以上
jū nen ijō
more than ten years