Congrats!
From the experience of being the gap kid (though I'm just half of yours--11 years younger than my closest sibling), the first couple of life stages he'll see you more as another adult and less as a brother; but when you both get older that'll change. I'm good friends with my siblings now that I'm in my mid 30s and they're inching closer to 50. I started to see my siblings more as actual siblings once I started to move beyond my teenage years.
