SuStel:

naH jajmeywIj bIQ'a' HeHDaq jIyIt
In my youth I walked on the beach.
My intention here is to imply that I used to walk on the beach;
it was my habit to walk on the beach in my youth

jIH:

If this sentence describes a habit taking place during youth, then
shouldn't the sentence be {qaStaHvIS naH jajmeywIj, bIQ'a' HeHDaq
jIyIt} ?
The way I would understand {naH jajmeywIj bIQ'a' HeHDaq jIyIt}, is
that "in my youth, once I walk on the beach".

SuStel:

The sentence could be interpreted as In my youth I walk on the beach,
but only if you're conceptually casting yourself back in time to those heady
vegetable days.

I'm rather confused here..

In your original sentence, i.e. {naH jajmeywIj bIQ'a' HeHDaq jIyIt},
your intended meaning was the stating of an action while conceptually
casting yourself back in time at that moment ? At a moment of a
specific walk on the beach, where a crab bites your foot ? An
action/event which took place only once ?

Or was the intended meaning that while you were young you were
habitually walking on a beach ? i.e. describing an event which was
happening regularly ? But an event you're actually re-living at the
time of the narration of the sentence ?

Or was the intended meaning, the description of a habitual event which
was happening regularly, but without re-living it at the time that the
sentence is spoken ?

The point is that there isn't a single meaning to a verb that doesn't have a type 7 suffix; it can be interpreted in lots of ways, depending on the context. You must apply the associated context to get the correct meaning. Two ways it can't be interpreted, though, are perfective and continuous.

Look, the rules are just what's in TKD. When an action described is a completed action, you must use a perfective suffix; you can't drop it. When an action described is a continuous action, you must use a continuous suffix; you can't drop it. For everything else, use no aspect suffix.

Completed or continuous from what point of view? Every sentence has a point of view that may or may not be the same as the time context or the speaker's present. wa'leS qaHoHta' Tomorrow I will have killed you takes as its viewpoint a moment tomorrow after my killing of you. "Place yourself in the moment after my killing you tomorrow. I shall now describe what you see: I have killed you." wa'leS qaHoHtaHvIS jImon While I'm killing you tomorrow I smile forces the viewpoint to be a slightly earlier point, still tomorrow, but during the act of killing you. It's specifically at the moment I smile. wa'leS qaHoH I will kill you tomorrow has right now as the viewpoint, and is looking ahead to a hypothetical action — being hypothetical, it certainly isn't completed.

-- 
SuStel
http://trimboli.name