
For completeness, the IRS will care about when property is obtained, since when you sell it, the capital gains tax rate is different for short-term gains (typically less than 1 yr) and long-term gains (typically over a year). It’s just that they don’t require a report when you acquire said property (unless it’s cryptocurrency, which might require you to answer a yes/no question on your tax return that year, even when merely buying and not selling).
Here in California, the term “dirt bike” essentially exclusively means off-street recreational vehicle. Some road-legal motorbikes will draw heavy inspiration (eg dual-sports like the DR650) or truly are dirt bikes with added equipment to make them legal, but these would be called motorcycles or motorbikes and registered accordingly.
Being able to ride one’s own two-wheeler from home to a vehicle recreational area in California is the domain of dual-sport motorbikes or certain smaller electric dirt bikes that are eligible for moped registration, both options requiring some level of license.
In Australia, are those rules consistent between all the states? I’m sure different US States regulate dirt bikes differently too, but it’s not something I’ve ever looked into in detail.