I don't think it's that simple though.
I "learnt" customer service skills as a volunteer for the local cats home at the age of 12. I then got my first paying job earning peanuts (years before minimum wage) and worked 4 hours a week in a sweet shop when I was 13 - over the course of 3 years, I progressed from cleaning out the empty jars and back cupboards, to serving customers on my own while the owner went for lunch in the pub next door! How many voluntary or paid work opportunities are there for under 16's nowadays?
At 16, I got a job in a High Street name clothing store; I learnt about stock control, display, electronic tills, H&S, card payments, cashing up etc.
School gave me opportunities to; visiting local businesses to ask for donations, running stalls at fetes, welcoming school guests etc. Thats not widespread anymore, either.
I've had 16 year olds in my shop who can't bring themselves to look at the customers. Who freeze when the customer asks them something, and who stand in the doorway preventing customers from entering. I've had to repeatedly remind them about the "no mobiles phones on the shop floor" rule; even though they've had "no mobiles in the classroom" rules for years!
When I was learning, I'd get an earbashing and told to buck my ideas up if I didn't serve quickly enough, chatted to friends or got in my bosses way. That's how I learnt. If I did that to the young workers I've had in my shop, I'd be reported for child cruelty!
Young people have fewer opportunities to learn the basic skills needed in the workplace, and apprenticeships are generally taken up by young people with lower academic attainment, who will have been less likely to be picked as "school ambassadors" or trusted to run the fruit stall, or a fundraising project at school (unfair, but true in the schools I'm familiar with). Couple that with the fact that many teenagers are not encouraged to interact with adults face to face and it can take at least 12 months to get 16/17 year olds to a point where they can actually do a decent job as a sales assistant or receptionist!