4AGE is the only option, but expensive with the cult tax. 1600cc, light on fuel, light in weight, gets you a decade ahead in engine design age, but it all depends on how worn that particular motor you get is. Needs a T50 gearbox, the KE70 should have come out with one right from the start.
You could hunt for a 5K, but they're a lot harder to find and a decade of design earlier. Even more-so for T motors, never so many on the road.
In the back of my mind I have Mazda MX5 for when the 4AGE gives up, there just isn't any other RWD 4cyl with a good gearbox anywhere. They can be 1.6L 1.8 or 2L, all in RWD. If you want to go to 2L, the Altezza 3SGE is popular, but its a very tall motor.