Hi, my husband and I are just into our 4th week in Perth, we like to think of ourselves as "young" still, 31 and 39! We are entering a transition though from work hard play hard to a more sensible living situation...Perth is not a real party town so to speak. However, like other posters have mentioned, there are some quirky and cool spots around, Freo deffo is one of them. Subiaco is a great town but it's something of a Sloane Street area with housewives driving dangerously about in their Land Rovers.
We are up in Hillarys and it's a great spot, not much nightlife but we've got everything we need within a couple mins walk, the marina is close by with a great Sunday Sesh type bar, beaches 5 mins away and fast ferry to Rottnest. I'd suggest anywhere within a 30 min commute to the City with buses nearby straight to the train stations, and with the exception of Freo, I'd suggest sticking to the northern suburbs. Scarborough, mt Crawley, Mt Lawley, West Perth. The rental market is very very competitive and if you only listen to this one thing of all the other cr@p I've written, is to rent via owners. Agents are rats. Gumtree is the best for this. Don't dismiss ads without photos either. We didn't and we ended up in a fantastic place with fantastic landlords. And, when responding to ads, do tell them about yourselves and your situation. And if you are in a position to do so, offer to pay 1,2,3 months in advance. Our landlady said we were shoe ins once she read our email, as every other respondent was very brash, asking more about what was on offer, when they could view, where were the photos, etc than actually being friendly, selling themselves and putting the owner at ease.
Best of luck with the house hunt! Let us know how you get on.