I have once worked for this business owner, which I've gotten pretty friendly with. The reason I quit is because his management style.
The problem: there is no ticketing system for the IT department. I once implement a very simple one - using paper on my computer or email, so I can track what problem I currently have, and what have I've done to fix it. Colleagues simply refuse to do so, and my complaint fall to the deaf ears.
After my resignation, it seems he has been more open to ideas and advices, and I would like to approach him to share better practices on establishing a solid IT department.
How could I propose these ideas without offending him?
Why I'm interested: I've been on friendly terms with the whole company, and I would like to see it mature. I'm interested in going back somewhere in the future after this company has become more organized.
Edit: I'm intending to invite him for a lunch together, and casually suggest ideas on him. However, I'm afraid of being seen as "teachy" as obviously I'm far younger than him by at least 30 years.