Theory of Relativity?

In the twins paradox when one twin who is speeding at nearabouts the speed of light will see
60 years as 30 years due to time dilation. Does this mean that his body will not age as much as the Twin on the Earth. How will biological aging be influenced by time dilation.

This is an excellent question because it forces one to consider how time is measured. Is time measured differently if you use a clock or if you use some biological process? Let’s see:

The twin that is traveling very fast does not know that time is passing more slowly for him than it is for his twin back on Earth. The twin on Earth does not know that time is passing more slowly for him than it is for his twin on the spaceship. In other words, for each twin nothing whatsoever has changed.

Suppose you measured time in terms of cellular divisions. In other words, suppose you and your twin measured time in terms of how long it takes for 1,000 cells to divide. Before leaving both twins measure this cellular division rate at 1,000 divisions per minute. So, having a device that can measure cellular divisions off you go in the spaceship.

As the twin in the ship measured his time in terms of 1,000 divisions per minute he would not notice any changes until he returned and compared the number of 1,000 cellular divisions that took place during his trip to his twin’s number. To the shock of each, the twin on the ship would, by the conditions set forth in your question, have half as many divisions.

Time is the unfolding of events.  Included in those events are all those biological events that support life and lead to aging... like heart rate, basal metabolism, etc.  So, yes indeed, the twin on the moving platform is actually aging slower relative to his sister back on Earth.  When bro returns after sixty years out there in deep space, sis will be sixty years older biologically and bro will be only thirty years older.

It's not only biological events that slow down either.  A metronome, beating out a steady rate, will slow down as his sister watches it from Earth (she has very good eyes).  The second hand on the platform's wall clock will fall farther and farther behind a comparable clock on the sister's office wall.  And the Rolex Oyster on the brother's wrist will run slower and slower compared to his sister's Timex as the platform speeds up.  [Note, the special theory of relativity does not apply while the platform is accelerating, but we can assume it goes steady state at each increase in speed.]

In case you missed it, time dilation is how we fly into the future.  [See source.]  In your example, when the bro returns from his trip to the star not quite 30 ly away (60 yr round trip), assuming he departed in 2011 and instantly gets up to speed, he will return to Earth in 2071.  That's to be expected.  But, this is important, his calendar on board the platform will read 2041.  So when bro steps off the ship onto terra firma back home, he will be thirty years into his future.  And all his family and friends will have aged thirty more years than he did.