I'd say that he purchase the jeep only if he paid the purchase price in full. 4 months is a little close to make $43,000 but if he's living at home he should be able earn it within the first year. By working very hard (2 jobs, night shift, hustle hustle). Check Valuetainment and other Youtube channels to get inspired then. GO WORK HARD. Remember new cars lose value quickly in the few years but if you want it bad. GO FOR IT AND SURPRISE EVERYONE...

But math is against you. you would have to work 18 hrs per 7 days per week at $20 per hour to make your goal. but you could easily make it before 19th birthday!