The expression 'flesh and blood' never denotes the substance of the body, but man in his totality as frail and perishable in his untransformed state (Mt.16:17; Gal 1:16; Eph. 6:12; Heb 2:14). It has the same meaning in I Corinthians 15:50, shown by the fact that in the parallel clause (v. 50b) the word corruption is used, which obviously denotes the whole man in his corruptibility and not the substance of his body.

it might be interesting to note that JW's take exactly the same view of 1 Cor 15:50 as yourself

"That verse could lead you to believe that somewhere in this world are some very old men! What does Christ mean? I believe what Christ was saying can be translated, "Some of you standing here will see the Son of Man coming in His royal majesty before you die." The Greek word translated "kingdom" (basileia) is used over 160 times in the New Testament. It is correct to render it not only as "Kingdom," but also as "the kingliness of the King" "regal splendor" or "royal majesty." The emphasis in verse 28 is on the coming of the King Himself in His royal majesty.
Unfortunately a chapter break was made by the translators at a point where it is important to follow the flow of the text. This same promise in Matthew 16:28 also appears in Mark and Luke. In all three cases it is immediately followed by the same incident, but in Mark (9:1-13) and Luke (9:27- 36), it is not followed by a chapter break. What the Lord was referring to in Matthew 16:28 is interpreted by the event that follows. Three of the disciples were about to have a private showing of Christ's glory.

Why, pray tell, would we be instructed to pray, "Thy kingdom come," if the kingdom is already here and fulfilled? And why would we be instructed to pray, "Thy will be done in earth, as it is in heaven," if His will is ALREADY being done on earth as it is in heaven? Of course God is ultimately sovereign over the affairs of this world, but He has called this age, MAN'S DAY (1 Cor 4:3). Hence, except for the sake of the saints, he does not generally openly interfere: He is presently allowing man to have his day - "that every mouth may be stopped, and all the world may become guilty before God" (Rom 3:19).

The problem is that most non-dispensationalists deny that Zechariah 9:10 will ever be fulfilled on this earth. They do not believe in a kingdom age as minutely described by all the prophets. They deny that the Messiah will ever rule this earth in a prolonged era of worldwide peace.