Someone who is licentious behaves or speaks inappropriately, usually in regards to sex.
What some might call a licentious senior citizen, others would simply refer to as "a dirty old man" (or woman). We usually talk about licentious behavior, but there also can be licentious photographs. Besides being inappropriate, licentious behavior is also usually regarded as immoral. If at all possible, therefore, licentious is a description you should seek to avoid for yourself.