Yes Target stores do have self checkout in them.
All Target Stores around should have self checkout as well as at least one or two cashiers.
The self checkouts at Target and other stores including Walmart have someone standing near them at another register where they control the self checkout cash registers.
If someone needs to be 18 or over to purchase an item then the assistant at the other register overseeing the self checkouts will come to the register and enter a password and then tell the self checkout that you're 18 or over.
So if you go through the self checkout and you buy beer or anything else that is age restricted then it will alert the attendant from the other register nearby to come over and check to see if you're of age.
Also be aware that for anyone thinking of stealing through the self checkout there is someone watching you to make sure you don't steal and there are cameras as well.