Do I need to keep my older cat separated from my new kitten when I'm not home?

Hey! I just got a 7 week old cat two days ago, and my 9 month old boy pretty much instantly fell in love with her. They were playing through the door on day one, and now it's day two and I had a supervised visit between them and they're playing and he's grooming her, so that's amazing! What I'm concerned about is how big he is. He's so big, and he tends to play aggressively, so while he's being incredibly gentle with the new baby, he's been doing this thing where he'll jump at her, and he's accidentally landed on her once or twice and made her hiss, and I'm just worried that he doesn't know his own strength. He's also pinned her down maybe twice, so there's that. It's only day two, so I'm not planning to let the baby free roam yet, but I just wondering at what point can I stop worrying that my well-meaning big boy won't accidentally hurt this baby?