I think what you are trying to do is very admirable but as other have said, most financial advisors deal with the bigger financial topics like mortgages, life cover, critical illness, investments, estate planning.
Here's a few basics you could try:
1- Get him to understand his payslip - teenagers often over estimate their earnings. I'm on £10 an hour so they automatically think £350 a week and don't consider taxes ir any other charges
2- Get him to start having as soon as he earns even if only £10 a week- he needs to set up a regular savings account with his bank
3- Get him to understand how much money he has, what he needs to pay and who much else is left. Use a spreadsheet our even just a page
£280 a week
£80 rent
£10 savings
£20 food
£10 transport to work
£10 phone bill
£150 to cover everything else etc
4- Get him to consider how long it will take to save purchase a pair of £80 runners if something, 8 weeks if saving a tenner, 4 weeks if savings £20
5- Explain the importance if looking for the vest price for something - search online, see if he'll get a better deal with student discount, does the store do bank holiday weekend specials, does he get 10% off if he signs up to newsletter etc
6- Explain that it is to avoid bad habits, gambling will destroy his credit record. Having his accoubt go overdrawn will too.
7- Suggest he watch some podcasts on money management.
8- Suggest he use the money management app thar his bank will probably have or get a bank that offer one
Then when he's earning a little more, he should book a free meeting with his student officer at his bank