Does anyone on here know how to tell the age of a Hobart Kitchenaid stand mixer?  I can't find a serial # on it, just that it's a K45SS and 250Watts.

Late 80's or early 90's.  The newest version of your mixer is 275 watts and has a 4.5 qt. bowl, older versions had a 3.5 or 4 qt. bowl, usually without a handle.  Lots of variations over the years with this "entry" model, some had handles on the bowls, some didn't.   

My mother had this model for a few years before giving to my sister.  I gave mom my 325 watt tilt-head model when I got my crank-up bowl 5 qt. model.  

Also, the "SS" designation indicates solid state speed control.  I don't know exactly when they upgraded to that, but I'd say maybe 10 or 12 years before Whirlpool took over. 

My non-SS K45 sports a slightly older version of the KA logo.  I don't know if the logo was updated when they went to solid state, but my guess is that it was somewhere around that same time.

The only other tag I can find is like a paper price tag stuck under the base, 528885 in purple ink stamped on it.  I saw where Target has Pro Series mixers factory refurbished for $199. 

I got the mixer pictured above at Savers for $29.99 a few years ago, complete with whisk, burnished flat beater and dough hook.   I switched out the burnished parts with coated ones so I can run them through the dishwasher.

The mixer needed nothing but a cleaning, and it's much quieter than a new one.  I put Dave's noisy KA Professional bowl-lift model in the basement and the K45 replaced it on the counter.  I prefer the tilt-head design. 

Thanks for the information about my mixer's age.  I haven't had much luck trying to use the logo to determine its age range.

KA/Hobart's switching to a beaded edge on the bowl was a major improvement.  My mixer was scratched up pretty good from that flat lip hitting the upper area on the riser portion of the base.   If you look closely at the picture below, you can see the area where I applied touch-up to the scratches.  I switched out the flat lip bowl with a later type that has a handle, as the clearance is so minimal that it's hard to avoid the flat lip scraping the painted surface.