I dont follow you
The doctor doesn't know the theory of relativity thus he assumes that the time on board flows in the same way as on the earth
He assumes also that his brother's heart still beats at 60 beats / minute same as on the earth
If the starcraft is moving away then he expects to receive a pulse every T = 1 + 0.95 = 1.95 sec
Of course the theory of relativity is valid regardless of the doctor's knowledge thus he will actually receive two next signals at a time interval T = 6.24 sec

What is the most natural explanation ?

The pilot's heart frequency on board is lower than on the earth as well as any other metabolic process
Thus the pilot will look younger on his return

No sorry the topic was clear and nett
I claimed that special relativity by itself entails the twin paradox
Joey did not agree

Again a little bit of hystori of physics

The twin paradox had been proposed by Einstein himself before the general relativity
Someone argued that the special relativity may be true , yet the paradox may be false
The reason being that the special relativity is valid only during the cruise phase
What does it happen during acceleration - turning - deceleration ?
In principle the acceleration phase may compensate the cruise phase so that on his return the pilot may have the same age as his twin brother
Nobody knew the answer at the time

This is the key difference between Joey's opinion and mine

I claimed that the paradox is true " Despite " the acceleration - turning - deceleration phases
Joey claimed ( at least this is what I understood ) " Thanks" to the acceleration - turning - deceleration phases

What Joey said is valid to explain why the pilot is younger than his brother on the earth
Why not the other way round ?

The different aging of two twin brothers is however a direct consequence of the relativism of time
If the time flows in a different way on the earth and on the starcraft, why should the two brother alwayes have the same age ?

In other words

Everybody knows that the special relativity claims that it does not make any sense to claim that two events are alwayes simultaneous
or that the same event has alwayes the same duration regardless of the observer
If so
Why should the twin brothers have alwayes the same age ?