You still get lockboxes from what I saw. I was 17 with like a 7 in the party. Whether you get just xp or boxes is dependent on the FATE ranking you get.

As for the OP, god yes. I'm 18 and my friend just started last night and I couldn't join him. Eureka badly needs a way to have the party either sync to the same level or allow higher members to sync to the level of another party member.