he also wants to pay off his mothers house. Houses are expensive.
Are they? I hadn't noticed?
Not that anyone overly cares about David Fifita's mother's finances, but just to point out how ridiculous your point was:
700k minus tax is still just shy of 400k take home.
If your living expenses were absolutely ridiculous for a 20 year old, say $100k (AFTER TAX!) a year that would still leave him $300k for the year to pay off the house. Most households with dual incomes and kids in Brisbane have far less than $100K of after tax money to get by on, let alone David Fifita, a single male in a share house who likely pays for f*** all given he's an extremely well know footballer in a one team town, not to mention he also has a football club that provides nearly everything for him.
If the median Brisbane house price today is around $600k, minus the 20% deposit, that at most means she owes about 480K assuming she bought the place literally yesterday.
As she's an older woman though, you could reasonably assume the house was purchased a little earlier than yesterday, when house prices were undoubtedly lower, so the balance would quite likely be well inside the $300k David Fifita has leftover from just one year of his salary.
It's a ridiculous argument to try and defend.