Have some good men been cut off in the midst of their days?
Yes.

He weakeneth my strength in the way; he shorteneth my days,
Psalm 102:23

But is this always in mercy?
Yes.

They are taken away from the evil to come,
Isaiah 57:1

Have some wicked men lived to a great age?
Yes.

The wicked live and become old,
Job 21:7

And is this always in judgment?
Yes.

For the sinner being an hundred years old shall be accursed,
Isaiah 65:20

But are good people of all others most likely to enjoy the comforts of this world?
Yes.

There is no want to them that fear him,
Psalm 34:9

And to live long in it?
Yes.

What man is he that desireth life, and loveth many days, let him depart from evil and do good,
Psalm 34:12, 14

And shall this blessing be granted as far as it is for God’s glory and their own good?
Yes.

There failed not ought of any good thing the Lord had spoken, all came to pass,
Joshua 21:45

And if denied in this world shall it be bestowed in the next?
Yes.

For this is the promise which he hath promised, even eternal life,
1 John 2:25

Is long life and happiness a blessing peculiarly vouchsafed to dutiful and obedient children?
Yes.

My son keep my commandments, for length of days, and long life and peace, shall they add unto thee,
Proverbs 3:1–2

And denied to the unruly and disobedient?
Yes.

There shall not be an old man in thy house,
1 Samuel 2:31