Passage
They shall still increase in a fruitful old age: and shall be well treated,
They shall still increase in a fruitful old age: and shall be well treated,
Psalms 91:13 The just shall flourish like the palm tree: he shall grow up like the cedar of Libanus.
Psalms 91:14 They that are planted in the house of the Lord shall flourish in the courts of the house of our God.
Psalms 91:15 They shall still increase in a fruitful old age: and shall be well treated,
Psalms 91:16 That they may shew, That the Lord our God is righteous, and there is no iniquity in him.
The verse centers on "shall", "still", "increase", "fruitful", "well", and "treated". It is saying that the verse draws attention to "shall" and "still", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 14's "They that are planted in the house..." into verse 16's "That they may shew That the Lord...", so "shall" and "still" belong inside that flow. In Psalms context, the local focus is worship, trust, the LORD's kingship, and covenant mercy.
A plain takeaway is to answer the verse's own emphasis on "shall" and "still" with trust shaped by these words, not by a vague optimism outside the passage.