I have personally never heard of the significance of 18 degrees of a sign.
I saw your chart in a previous thread in which, unfortunately, no degrees of planets/house cusps are provided. Calculation wise, I can't make out what is where.
Saturn represents 'the limitations of the physical body'. I.O.W, how much one can take without breaking, through the sign in which Saturn is placed, could effect the area of the body ruled by that sign.
It is the planet of outer versus inner authority, obligation, control, that is sometimes produced by others. 10th house is suggestive of a parent, boss, government body, etc.etc.
Saturn has strong associations with those disorders that can become chronic over time.
Natal Saturn is in Gemini. Gemini has rulership over the nervous system in all its facets, mental as well as physical.
Any harsh aspect between Saturn and another planet could effect (mental) health.
Saturn rules Capricorn, yet is also the traditional ruler of Aquarius. When natal Moon receives harsh aspects, it could be Saturn of Aquarius that is involved.
The chart shows Aquarius on 6th house cusp, associated with physical work, yet can relate to physical disorders when not applied as is necessary.
There appears to be a Moon opposing Neptune in the 6th house, which could relate to an emotional instability. Moon appears to be in a 45 degree aspect to Saturn, and Saturn appears to be in a 135 degree with Neptune. All are considered predispositions toward 'disorders' if their energies are not used as is their intent.
Yet when Saturn in Gemini is able to 'strengthen' the nervous system by its ability to accept the evidence of physical facts (with help from Mercury in Taurus, Virgo Asc.) regarding the reality of life, through cause and in spite of difficult situations a person faces , any physical illness(es) need (Moon) not get through ( Neptune) to affect the physical body.
From your age, you are young enough to change any course you find is not working for you.
I have a 17'33"-18'00" Cancer rising or my ASC is at 18th degree (actually at 17), including the sun sign's name Cancer and the sign ruler the Moon is conjunct my natal sun in 8th Aquarius to gave me bad vibes on what could it mean in horary predictions, and the traditional ruler to hold a high and strong malefic power like Saturn is in my natal sun and moon sign for 2.5 years from late 2020-early 2023 and it turns out I had a mild covid case in Jan 2021 but I expect to receive my 4th and last shot of the covid vaccine by Dec 2022 at the earliest.
You're probably referring to Degree Theory which I believe was largely popularized by Nikola Stojanovic. 18 degree is a Virgoan degree and going off his example with the carpenter making the bed for his wife, it adds a minimized accent to the planet / sign. 22 degrees is the "kill or be killed" degree of Capricorn. It doesn't always or literally mean death, but rather an overtone of fighting for survival regarding a matter or thing.
First of all did you read the sticky, in this sub-forum for Degree Symbols, about understanding the enumeration of the degrees?
I doubt that you did otherwise your query would've been worded correctly.
Is Saturn in the 18th degree [never mind what Sign] or is it in fact in the 19th degree?
If your natal chart shows Saturn to be at exactly 18° 00' 00", then you may say that it is AT 18 degrees.. Anything more than that is, in fact, in the 19th degree, anything less, down to, and including 17° 00' 01", is in fact in the 18th degree.
Secondly, what you are asking about is not about Degree Symbols, but rather the alleged nature of a certain degree... but as it seems this is a mistake that is made about once or twice a year here at this forum, and you are obviously newly arrived... all I have to say any further is, Welcome aboard. If you have any similar such questions in the future try looking through the various other sub-forums here at AW and see if one of them might be appropriate?
If you don't think there is one, then might I suggest posting such a question in one of the natal astrology sub forums?
I'm not a moderator here, nor do I have any connection with the administration, but Degree Symbols is kind of my "specialty", others might say it to only be an obsession, but whatever one might wish to call it, I do like to see that this sub-forum doesn't get cluttered up with threads that don't really belong here. That way the relevant threads don't get buried further back into relative obscurity.
I do have an opinion, or actually more of a comment in answer, that comes from nearly 38 years of determined astrological studies and a lifetime of experience with matters concerning spirituality and humankinds' existence, to your question that may be of help, however?
That is, there is nothing in the Heavens put there by our Creator that was placed there with the intent of being malevolently harmful.
What does cause us grief is due to our own karmic indebtedness and there are those objects, and aspects, that will mete that out.
I hope that I have been of some help to you towards becoming greater in astrological knowledge and becoming more adept at becoming, or being, an astrologer yourself.
Fear not... as for what my signature line says is quite true.