[strike]Do I[/strike] Can/Should I say "We are the same age" or "He is the same age as us" or "He is the same age as I am"?
You need to separate the sentences you're suggesting more clearly. Remember that "Do I can" is not a grammatical way to start a question.
Can I also say "He is the same age as ours or mine"? (Don't put a question mark and a full stop.) No. He is the same age as us. He is the same age as we are. He is the same age as me. He is the same age as I am. Remember that although many other languages use "to have" (or their equivalent of it) with age, we do not. Consequently, it makes no sense to use the possessive.
I hope I have not made any grammatical or capitalisation mistakes.
I have one more question - "He doesn't take it on board". What does it mean?
It means "He does not take any notice/he does not act on the advice".