Sage has two parallel meanings. The first is "wise" — from the Latin sapere (to be wise), giving the English noun "sage" (a wise person). The second is the herb sage (Salvia officinalis), used for cooking and traditionally associated with healing and wisdom.
Sage as a name is unisex but used about 60% for girls. It entered the U.S. top 1000 in 1991 and has been rising. Today it sits in the U.S. top 175.
Sage does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Sage reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.