An immigrant to any country who immigrated to a country while they were young. Stroller immigrants can be legal (Had their health and criminal records checked and allowed into the country) or illegal (Overstayed their visas or sneeked into the country), but usually, they're legal. They also adopted the culture of the host country to varying degrees.
Sanjay: Dude, I'm from another country. I know what it's like to be an immigrant.
Taylor: You came here when you were 5, Jay. You're 35. You've been in this country longer than I have been. And I was born here. You used to play lacrosse in high school, you're the best snowboarder I've ever known. Your curries taste blander than tater tots. And to boot, I saw you play cricket with your family. They're always complaining about how you hold a cricket bat over your shoulders like a baseball bat. They had to say it in English because you don't speak a word of Hindi.
You're just a stroller immigrant. You're really an American at heart. Now let's go get some pizza, Jay
Sanjay: You're right, Taylor.