Make your decision.

You can deliver an enthusiastic yes, or you can explain why you’re not the right person for the role but can help the young person think it through and find someone who is a good match (assuming you can actually provide this sort of assistance). There is also a third option that allows you to treat the request with the seriousness it deserves. If, whether for personal or professional reasons, you just can’t serve as a mentor or offer the young person help in finding one, be direct and explain why in as much detail as the situation allows. In this circumstance, as in many others, a short no is better than a long maybe.