John Gill Commentary Psalms 71:5

"For thou art my hope, O Lord Jehovah: [Thou art] my trust from my youth." — Psalms 71:5 (ASV)

For you [are] my hope, O Lord God
The object, ground, and foundation of it, even of present deliverance, and of future and eternal salvation;

[you are] my trust from my youth ;
in whom he trusted in his youthful days, of which there is an eminent instance in (1 Samuel 17:33–45) .