When to potty train a boy

How did you know it was time to start potty training your son? What were the signs?

My son is almost 15 months so he’s got awhile but I am just wondering if he’s getting to the point to where he knows he’s actually wetting his diaper. I’ve caught him pulling on it and tugging on it and shortly after I will see the yellow line turn blue indicating he just peed. He also went behind our sofa and was pulling his diaper off the other day. Thankfully it was just wet and not dirty because we would have had a huge mess. Are these normal toddler things to do or is he showing signs of being aware of him being dirty or needing to potty? I’m a FTM so sorry if I sound very uneducated on the topic.