The short answer is always, "the lower the better".  The full answer is more complicated but effectively breaks down into, 1) the Manufacturer's historical quality of vehicles, 2) Known issues with the given vehicle model / type 3) The driving habits / patterns of the prior owner(s) including any Off Road / 4x4 and Trailer towing 4) The Maintenance habits / patterns of the prior owner(s)conditions of the vehicle including Maint. records. 5) Is the mileage from Highway or around Town driving (Stop and go traffic or easy highway traffic)?  Usually you want easy highway (not stop and go traffic, especially on an automatic trans) and of course 6) The actual mileage on the vehicle itself.

----- After determining the above (if possible), a good rule of thumb is to take the age of the vehicle and multiple by 10K, 15K and 20K.  This will give you a per/year lower end mileage, average mileage, and higher mileage.  So, for example, it's only the start of 2021 so we'll use 2020 as our current complete year as follows:

2020 - 2004 = 16Yrs old vehicle

16Y x 10K = 160K - Lower end mileage  = Anything near this is your target mileage is good (lower even better).

16Y x 15K = 240K - Average expected mileage for a vehicle this age = Engine should be OK, may need some Maint if not abused but it's a bit high and Although I've seen very high mileage (300K + on some Toyota automatice transmissions, I would shy away from this unless you're OK with swapping a trans yourself or get the vehicle for a (super) awesome deal (say $1,500) and don't mind dumping $1,500 - $4K for a transmission (price depends upon if you do the work or someone else does it for you.

16Y x 20K = 320K - High Mileage for this age of vehicle.  Although it's a Toyota and may still run well (and assuming the vehicle was not beat) this mileage is high and I expect major Maint. at minimum to be required (even for Toyota) and likely other mechanical service such as transmisison and I would steer-clear of this high mileage vehicle (unless you want a quality project vehicle (at a very super price - Like Free)

Recommendations:

You said, "...my first car...", therefore I recommend the following:

1) For Auto transmission - Don't go over 160K if you can help it (maybe... 175K-ish max)

2) Be patient and wait for the right car and mileage.  Stick to your target mileage and price. Don't jump just because you want a car (unless) the deal is GOOD and you can afford it.

3) Purchase the 2.4L (4cyl) and not the 3.5L (V6) engine.  Although there are no major issues with the V6, there are a few nuisance issues with V6 models

4) Consider the 2006 2.4L (4cyl) as I think it has a bit more cabin space and is more comfortable to sit in and low mileage range would be near the 140K-ish range :))

5) Learn to drive a stick (seriously) as the manual trans literally pretty much last forever (clutch maint. still required) and if you can drive a stick, you can drive anything.  It may take time and careful practice but well worth it.

Here are some good examples with lower mileage: https://www.carfax.com/Used-2004-Toyota-RAV4_z29445

PS, if you buy one, maybe post a pic here so we can see it.

Good Luck!