Hello. You are correct. It can be both psychological and a physical problem. The psychological stress and other functioning also plays and important role in maintaining the erection and ability to delay the ejaculation. There are certain conditions which can lead to early ejaculation like injury to lower back or trauma to the groin region. More than 10 strokes means an intact system.
There are some simple measures which can address the issue. Regularly do workout like Yoga and pranayama, oi application to full body followed by warm shower, good nutritious food are essential.