Indeed. Especially after 6 years. Even a lack of thermal compound would increase your temperatures by only maybe 5C. This is definitely dust buildup.
What you need to do is have someone clean your system. Or, if you are comfortable, you can do it yourself.
Get some cans of compressed air, open your computer and blow the dust out. You might want to do this outside. Hold the fans so they don't move when you blow at them. You'll want to get everything off from between the heatsink fins especially. I can't advise using a vacuum cleaner because most build up static electricity on the plastic attachments, or so Cisco tells me. I've used them in the past with no problems.
That 73C is between "too hot" and "way too hot" depending on your CPU model. 61C idle is definitely not right. But that 64C is a normal temperature for most graphics cards. Actually, most higher end ones run hotter on load. Mine is a 3870 and runs at an impressively cool 67C load. Most usually run into the 80s on load.