Zentangles are not age specific, and can be done at almost any level drawing skill. The idea of zentangles is doodling as an exercise in relaxation and mindfulness.
Zentangle art projects are space filled with lines and patterns. While it is intended to be a structured and focused activity, the process is flexible. Some patterns are challenging and complicated, but many patterns can be made from simple shapes. Some examples are grid patterns, curving lines or repeating letter shapes. The iconic look comes from using a fine-point, black permanent marker on white cardstock, or heavy paper, but these elements are less important than that of self expression through non-objective drawing.