A few years is fine, but it’s worth keeping in mind that if you want to emigrate to Australia as your partner’s de facto spouse, you may be asked to prove that your relationship is bona fide.
This means producing things like photos of the happy couple, airline tickets to demonstrate holidays taken together, utility bills paid in both of your names and joint bank account statements.
I know one couple that were asked to attend an interview to establish that their relationship was for real.