That's a 23 series at the very oldest. I can't see from the picture, but it should have the Whirlpool power module assembly, which first appeared on the 23's.
It's a very capable machine though, and there are some here who feel Whirlpool's power module provides better results than Hobart's design that was last used on the 22 series.
I bought and installed this very machine in my parents house back in the early 90's. The only complaint that I ever heard on it was that it seemed to spend more time heating water than actually washing. Mom always thought it was broken and was afraid to leave it running on its own.
Yes...it takes about 25 min to heat water up....I thought mine was broken too and only used the non heated cycles...but when it heats the water it does a great job!