2 years with lots of bumkum building up is a long time. I suspect you have installed and now deleted quite a bit of software over that period. One really simple thing you can do is to set-up a new profile, boot from that profile and see if it is faster (Apple > System Preferences > Accounts > +). If it is then back-up your data, switch over to a new profile, restore your data to the new profile, delete your old profile, rename your new profile.
Another thing you can do is to delete your LoginWindow preferences (the files that tell your computer what to load at boot up). Look in Library/Preferences or [username]/Library/Preferences. Delete com.apple.loginwindow.plist and loginwindow.plist (if one exists). Also delete any plist file in this directory that relates to software you no longer have installed on your computer. Don't worry, if an app needs a plist (preference file) and doesn't have one, it will just recreate it. I'm pretty agreesive at clearing out this folder.
Now look in Library/LaunchAgents and Library/LaunchDemons deleting any thing that is running that you don't want to run. I have nothing in these directories except com.sophus... and com.microsoft.office.licensing... You can always add a start-up program again under System Preferences > Accounts > LogIn Items.
Reboot.
Now download and run Onyx. Run all the maintenance scripts.
Reboot.
You're welcome.