We're in the States, and DS attends a school that's PK-12 (so that's ages 4-18). DS is in Kindergarten, which is ages 5-6. There is a Senior-Kindergarten Buddy program, which 'buddies up' each kindergarten student with a senior (ages 17-18) for the year.
The school organizes S-K Buddy activities (reading, fun sports etc), and it's just one hour per week, plus one big event each month. December's was a 'Happy Holidays' party.
DS adores his buddy, and even felt able to confide in him about an issue he was having with another student, and the buddy spoke to the teacher about it. It was dealt with. I've met him a few times, the first time was when he came up and introduced himself, and he's a lovely young man. I'm not surprised he's been accepted early action by Yale!
The 'buddy program' has never concerned me, not once, although a few friends (both here in the US and back in the UK) have recoiled in horror at the thought of it. What they think happens I don't know. It's all supervised, it's never a case of the senior and kindergartner being left alone together, it's always a group thing.