Note: Paul talks about adjectives and past participles. I would say that most, if not all, past participles can be used as adjectives, so it’s not really necessary to distinguish between the two.
This can be seen if we look at ‘get’ as meaning a change of state or condition:
I was single, then I got married. Now I am married.
I was young, then I got old. Now I am old.
‘I am married’ – ‘married’ is an adjective, from the verb ‘to marry’