@oscar07 - WELCOME - y buena suerte desde el extremo nor-oueste de escocia!  LOL you are NEVER too old to start dude !

I, as all our members here, wish you total enjoyment on your journey - you have a good violin/fiddle in your hands there - enjoy and share your learning experience !  And never hesitate to ask questions - there is no such thing as a "stupid question"...

Cheers, Bill

...hmmm many reasons - I'll go back to my beginner days - "out of tune" is "normal" until you get the fingering correct - don't worry about that.  Screechy and scratchy is different.  What I did find was that open string bowing was OK - I found the same once I stopped a string on the fingerboard.  I "uncovered" two things - 

(1) The open string has a "really solid" endpoint at the nut.  Under your finger, it's a bit "softer" and a bit more "damped".  The open string will always "ring louder and clearer" (for want of a better description) than a stopped string.  The pad of your finger is not as solid, or hard, as the open string passing over the nut.

It is "very easy" ( LOL - sort of ) to bow repeatedly on the open strings.  With a "fingered string" - well - what I found - was - I had to be "conscious" of what I was doing - play an open string "less hard" - sure - it will end up screeching.   

I am aware of the "open string" sound now - it can often be "out of context" (well depending on the style of music and the particular piece you're playing) - and I sometimes feel it is "not right" - or have to very intentionally play it "softer"

(2) Bowing - it can be very easy to "slightly hit" more than one string at once- you may not be playing a "full double stop" intentionally - but if one side of your finger is touching an adjacent string, and the bow passes over it - you get this strange scratchy/buzzing sound.   On a four-string bowed-instrument  there are 7 "planes" your bow should move in - on the G, the D, the A, the E and three more - where you intentionally play (not necessarily open) two adjacent strings at the same time....  that MAY just be what you are (un-intentionally) doing....

It is TOTALLY impossible for me to be specific about this - it comes with practice - but I kind of think the way I cured it was to be "a bit more aggressive" with my bowing - none of this "gentle touch" that makes the open strings ring out - get a bit more "attack" into it.... of course - NOW - to my ear - I find the open string sound often too resonant and present compared to the rest of the notes I'm playing in a piece - of course - you can play the same note on the next lower string a bit further up - and then it "blends" better.

One of these days I'll master higher positions on the strings - getting there !

Cool.  That just comes with practice ! LOL   We all play "out of tune" to a lesser or greater extent - getting the finger position repeatable to within fractions of a mm is not easy.   I don't recall who said this - it was a very famous violinist though - "of course I play out of tune, it's just that I correct so fast, no-one notices" - or words to that effect.... 

It gets worse if you have different instruments with different nut-to-bridge lengths ( my EV is about 7 mm longer nut-to bridge than my two acoustics - and the bridge position is fixed ) so my fingering has to be marginally different - but somehow, you just get used to it - as you gain familiarity with each instrument, you just kind of "adapt" automatically.

I haven't done this, although I do have a clip-on "Snark" tuner - but some folks do use that ( other clip on tuners are available - LOL ! ) during their initial learning.  I neither advocate, nor disapprove of the idea - I guess it can be useful.  Just a thought.