How a 20 something year old staying alone spends his/her money is different from how a 20 something year staying with their family or guardian spends their money. The former has more financial obligations; rent, food, utility bills, et al. This means we are looking at a 20 something year old who is making money and not giving 30% to rent, and a further 10% to utilities.
How best should such individuals manage their money?