Child. Difficulty In Paying Attention, Frustrated, Not Following Instructions, Forgetfulness. Signs Of ADHD?

my 4 year old boy has some trouble paying attention, gets fusterated when i ask him to. He makes a alot of mistakes, when i ask him not to do something he says nothing then does it again. He gets bored easily and continously taunts his 3 year old sister. He gats very aggressive at times. He even tries to annoy me when he gets bored. I try to entertain him by colouring, baking, and playing outside with new things but he will only be interested for a few minutes. When i talk to him he doesnt look like he is paying attention to what i am saying. He conatantly forgets where he puts things, like his favorite teddy. I tell him not to do something like going outside by himself cause he could get hurt and he keeps doing it. I tell him that it could be dangerous. He tries to constantly wander off with strangers when we go for walks. He trusts anybody. I keep repeating myself but he doesnt listen. My friend has 4 kids that are older and i take my boy to her place and she noticed how he acts and thinks he has ADD. Can somebody please help me by telling me if these are signs of it?