Based on a home page which sells oregano oil (origanum vulgare),
<a target=_blank class=ftalternatingbarlinklarge href="http://www.herbalremedies.com/ordilesoil.html">Oregano Essential Oil (Oraganum Vulgare)</a>
it indicates that putting a few drops in a towel, etc., and breathing in would help with sinus infection, but does not indicate anything regarding age range. It does indicate that it is diluted with olive oil, and direct contact to skin may cause irritation, so I'd recommend diluting it with a little extra olive oil, and continue to prevent contact to skin.