It's one thing to offer advice based on your past experiences, but it's quite another to call him foolish and irresponsible. Get off his back.
How many of you bought your house, car, or plane with cash? An airplane is a toy too. Why would you not pay cash for it?
How about because it costs more than you have currently have and you would like to take advantage of it before you die?
Admittedly, a motorcycle is more of a "toy" than the other purchases. I purchased my cars either cash or on "zero" interest. And I keep them until they rot out from under me.
As to 250K/year not being enough to live on in 30-40 years, poppycock. It will certainly not buy what it does today, but it will certainly be a good start. A very good start. With reasonable financial planning, you can easily make it on much much less. You are speaking to a wide range of income earners. Some of us own planes, multiple houses, cars, motorcycles, and we did it on less than 80K per year combined household income. I'd absolutely love to make 250K a year. But I do not, so I have to make due with what I have. True, we don't spend on anything extraneous, but we don't go without. We spend most of our money on helping out the kids and grandkids. And we have enough to do that.
Don't force your brand of financial "wisdom" on everyone else. Be happy for the guy and congratulate him on his new "toy."
Be careful riding it, though.