Ok, just another suggestion to throw into the mix:

Stop nagging. Immediately. By nagging you are helping him to tune out. He is subconsciously confident that you can be relied on to do his thinking for him. Your reminders are like a crutch... you need to remove the crutch and let him fall down. You might think that he won't be able to think for himself but he will if there are more negative consequences for tuning out. He has to learn to associate "tuning out" to "missing out". So let him tune out and let him suffer. It's the only way that you will stir within him the desire to be forward thinking. He needs to know that there will not be a reminder. He needs to be worried about forgetting.

My DD was starting to go down that path. Like my DH she was starting to show signs of becoming a bad time manager. It was noticeable each morning as she was trying to get ready for school. Because she was given a lift to school by DH on his way to work he constantly nagged her and beseeched me to do "more" for her so that he wouldn't be late etc. At first, because I wasn't working I didn't mind... and did more. But one year I returned to uni and needed to be out of the house early myself to attend lectures. I made it clear that i was not available to help nag DD each morning. I stopped getting involved. DD was at an age that she was capable of doing everything anyhow... even making her lunch (she was 6/7 yo). I actually noticed some improvement. But the biggest improvement was a few years later when we moved house and she had to get HERSELF to school, as well as make lunches etc. I tell you what! Because it was her sole responsibility to get herself to school she then realised that it was totally up to her. I had a new baby... I often didn't even get out of bed each morning... it was just a kiss as she left for the day. She was never late for school. No one nagged, she just knew that the buck stopped with her. These days her time management skills are better than the average child her age (13). She thinks ahead and does what needs to be done at the right time. All because I wasn't there to nag.