jrhartley's comment is hardly a fair one, or perhaps it is for his own experiences. No one can teach you how to design. You are guided, and the smallest guides you are given help you to understand why you might be doing something; designing can't be taught from a book. At my school we have many private conversations or 'crits' every week in order to determine the direction we are taking and of course to ensure that we aren't doing anything terribly wrong. Architecture is a complex profession and there is a lot to learn but you seem to have a strong skill set that will really stand to you. These are skills I would love to possess but unfortunately school doesn't have the appropriate facilities to do so. Well actually we do but they don't use the,.. that's beside the point.
As a mature student it's very important you choose the right school. Don't rush into it. Since you're 35 and possess the skills you do, you will have a very particular way of thinking or what schools often refer to as a 'school of thought'. The worst thing would be to go to a school that didn't allow you to practice the way you would like to or what you believe in. Your chances are as good as anyones - as long as you first demonstrate that you have passion And secondly the ability. I definitely wouldn't show the panel interviewing you in a university any construction drawings, and I'd keep the sketchup models to a minimum. Schools are looking fro students who have good observational skills. If you really want to do this it might be worth your while taking some time out and doing a portfolio course, or if you think you can do it without the help then do - they're looking for obsessive observation. So say you draw an avocado - try and find different ways of representing its texture, draw it many times in many different ways. Find ways of reproducing paintings or beautiful drawings.
This is my advice from Ireland - our 5 schools here are not dissimilar - there maybe universities in the UK who enjoy sketchup models etc. However I would only use them to demonstrate your interest in design and not look what I made isn't it beautiful. Sketch up models usually aren't and we've been told it annoys them. However you're definitely what they'd call an 'interesting candidate' so your chances maybe better than anyone elses. Good luck.