Tell the young man you will hold it for him and for him to save up enough money to buy it (you determine a very fair price) then in 6 months or so ask him how much he has saved up. If it seems that he is really trying to save up the $$ then do what you feel is correct.

I have done something similar in the past. I told a close friends daughter that I wanted XX for a car. In 6 months I asked her how much she had saved up and she had about 1/2 of the $$ saved. I told there that was fine and to bring the $$ she had and come pick up the car. Talk about a happy young lady.

Would do it again in a heartbeat.