Concrete symptoms of over-engineering

I have recently found myself in the position of explaining an (In-House) application I have written to two candidates my company likes to hire in order to assist in maintenance and adding minor features.

It is the first "production" application I have written, it has 45k LOCs and I spent almost two years of "solo" development on it. I am fairly young (18) and wrote the application from scratch while being contracted as stand-in for a former developer who left the company. Unexperienced in designing applications of this size, I tried to use common architecture- and design-patterns.

Today I know I have done some serious over-engineering, e.g. using a disconnected change tracking architecture instead of the Unit Of Work pattern, which the chosen ORM has already implemented. I will probably never have to go "real" three tiers.

Both candidates have 10 years+ background in In-House Application Development with the relevant platform. Being half their age and having little experience I do respect their opinion. When I was explaining the application architecture to them, comments were along the lines of:

Jeez, no one would pay me to do stuff like that, I have to get things done
Stick with what the framework does, don't use fancy libraries/technologies
Don't wrap framework code. On a team, everyone will write his own wrapper code anyway.
You're using .NET 3.5? Well, we are using 2.0.
What does that LINQ stuff buy me? All this query composition and projection seems too complicated.

Now I am asking myself:
Am I an architecture astronaut? How do I know I am going too far with architecture? What are common symptoms of over-engineering?

Solution

What are common symptoms of over-engineering?

Code that solves problems you don't have.