Hi Sugar,
yes, this could well be an OCD obsession. It is very common for OCD sufferers to become obsessed with looking at certain types of people (e.g. men; women; children; old people; family members) and then ruminating over and over about whether or not they are attracted to those types of people; and whether or not they are aroused or excited.
These are very common obsessions. If you find that you are thinking and worrying about looking at people's groins / chests / other parts, and you spend a lot of time doing things like avoiding certain situations, certain types of people, and going over and over in your mind that you might have done something wrong, or they're might be something wrong with you, then you may well be suffering from an anxiety disorder.
Avoiding certain people or situations can sometimes indicate Social Anxiety. Carrying out mental compulsions (e.g. ruminating and checking), and avoiding people that cause you distress, can sometimes indicate OCD.
In order to find out whether or not you are suffering from OCD or any other type of anxiety disorder, you can go to your GP in the first instance. Explain the things that are distressing you, and tell them how much the distress and avoidance behaviours are affecting your life. You can ask the GP to refer you to a mental health professional for an assessment.
You can also read the excellent information packs on the OCD Action Website. Click on "Resources" on the top right-hand corner of the homepage, then scroll down and look at the list of info packs. (Packs such as "What is OCD?" and others might be helpful to you.)
You could also read a book about anxiety disorders. A really good book is "Teach Yourself Cognitive Behavioural Therapy", by Christine Wilding and Aileen Milne. (RRP £10.99) This books explains all of the common anxiety disorders, including Social Anxiety and OCD, as well as others.
You are not necessarily suffering from OCD or any other anxiety disorder. But the symptoms you describe are very common OCD obsessions and compulsions, experienced by lots of OCD sufferers.
(It's not the looking that's the OCD part. It's the ruminating, the doubting, the mental checking, and the avoidance, which indicate possible OCD.)
Look around this website, and go to see your GP if you are feeling worried or distressed.
Take care.