The best managers of younger employees are people who would otherwise love teaching for a living. They prize helping others grow and tend to overexplain their reasoning for decisions. Rather than assuming that twenty-somethings possess enough experience or perspective to read between the lines of their choices, these managers take an extra few minutes to lay out pros and cons and diagram their rationale. Three short minutes of explanation usually make excellent junior employees excited, since they feel the immediate benefits of gaining insight into decision-making processes. It also makes them better at working for you and your company, because it teaches them how you think.
Really excellent managers of really excellent young people also set up regular teaching sessions for them on different parts of the business. Top companies do rotation programs for promising younger talent. It's hard to support systematized rotation in small companies. But small companies can set up mini-workshops to expose highly promising younger employees to different parts of the company. Early investment of this kind yields payoff fast.
Here are some other good ways to motivate and teach young employees: