You should deep clean your mattress every 6 months.
Of course, if you spill something on your mattress, you should clean it immediately before the stain sets in.
Using a quality mattress protector will reduce the need to clean your mattress as frequently.
Deodorizing is when you get rid of odors from stains, spills, allergens, sweat, dirt, dust mites, and more.
It's a good idea to deodorize your mattress at least once every 6 months.
If you experience frequent night sweats, you may want to consider deodorizing even more often.
Mattresses should be replaced every 8 to 10 years due to wear and tear and for hygiene as well.
Mattresses overtime collect bodily fluids that soak into the mattress making the mattress gross so replace your mattress at least every 10 years for hygiene purposes alone.
You can help keep your mattress cleaner by using a mattress protector that you can take off and wash so you may be able to extend the life of your mattress with a mattress protector but either way the mattress should be replaced 10 years and it should certainly be replaced after 12 to 15 years.
I replace my mattress every 10 years and get a new bedroom set as well during that time.