Hi all, I'm about to finish my PhD in a scientific field in a few months time (if all goes well). I've recently submitted my thesis to get some feedback from my supervisor before I send it off to the examiners officially. Hence right now I'm just waiting...

However I am seriously worried about my career prospects after I finish in a few months. My time during my PhD was unfortunately not an enjoyable one. I did not receive any mentoring or any guidance from anyone unlike other people in my cohort did. Anyway, whats in the past is done, I am aiming to move on forward with my life. Because of my bad experience during my PhD I have been completely put off from doing a post doc, which was perhaps my original goal. I unfortunately don't think my supervisor will write a good recommendation letter either so I wouldn't be able to stay in academia even if I wanted to since most universities require academic references.

Anyway, I have been looking at jobs in industry and I honestly don't know where I'd fit in because no one has told me whether I'm good at this or that. I have some basic programming skills since I had to use it extensively during my research. But it is no where at the level of computer science graduates and software developers. I appear to be grossly under-qualified for most job descriptions I've looked at relating to entry level programming related jobs in data science, research etc. Since I'm now approaching 30, I'm probably too old to get into most entry level graduate jobs since those are mainly advertised to recent undergraduates who would most likely be 21 - 22 years of age...

Anyway I look forward to your comments and/or advice. Feel free to privately message me if you don't want to post anything publicly.

30 is too old? Are you kidding? Why do you care about the age of other graduates?
Anyway, just write an honest well written cover letter for jobs you like. Once you have a kick start, the wheel will turn on. Good luck.

There is no age limit for things like programming jobs and 30 is a very young age indeed.
From personal experience I can tell you that you are mistaken about the quality of computer science graduates. Most programmers are not computer science graduates anyway. They come from a wide range of disciplines and most of them are crap to start out with.
What matters most in software is experience. You have some. What you now need is to spend a month or two systematically learning your chosen language or languages from the ground up. Almost nobody bothers to do this and so they end up severely limited in what they can do. Don't be that person: do it properly, buy some books, work ALL the problems. From that you should find sitting tests at interview fairly easy. Also make sure you start creating a batch of cool programs to show what you can do.
This is almost exactly what I did more than 20 years ago and I was only a couple of years younger than you when I started.

While I agree that phd projects can be too focused and lack the other skill sets jobs may want remember that you don't have to have every skill listed, just proof that you have the experience and ability to fill the role.

The actual skills learned during the PhD process outweigh the skills of a fresh grad. Don't forget that the completion of the PhD is evidence of project management, the ability to produce an output within a deadline (assuming it didn't take you longer than the expected PhD time!). Conference organisation is evidence of delegation skills, networking. Conference presentations are evidence of having confident presentation skills and the ability to tailor knowledge to a varied audience (great if they are looking for a bit of PR.) Any committees that you served on work as evidence of team-work.

I am creating two resumes, one academic and one for the industry, and job hunting for both sectors in a month or so. This is a great resource for creating a CV tailored for the industry that showcases how to write an effective CV if you have a PhD and want to highlight what you have to fit the criteria:

https://www.state.gov/documents/organization/234524.pdf