Well, I'm from Castlemaine (actually, campbells creek). You're welcome to join me sometime.
I'm certainly not a super fit individual, (read: very overweight) but get there just the same.
My usual training ride is 40km to Guildford, Newstead and back again (usually average around 23 km/hr)
I also do a circuit around Vaughan and Guildford, 20km of steep short hills... but pretty (average only 19 / 21km/hr on that one)
When I don't have much time, I just 'whip' down to Guildford and back... 15km (average 24km/hr).
A nice day ride is: Over the summit of Mt. Alexander to Harcourt (Morning Tea) then to Maldon (Lunch), Newstead (Afternoon Tea) and then home. About 90km including a semi- serious mountain. I only do the 'Mt. Alexander challenge' once a year, and average only 18 - 20km / hr on that one!!