The grey line between adjectives & past participles and passives
Summary: The use of past participles as adjectives in English
Although past participles used as adjectives are passive in form some of them or more precisely a few of them can have an active meaning as in: a retired teacher. The word adjective is a bit ambiguous because there are two types of adjectives: an attribute and a predicate. However, whether the adjective is an attribute or a predicate it can be either the enemy of the noun because it is a subjective view / of limited perspective or the friend of the noun because it adds information.
Most adjectives are used attributively i.e. before nouns: a retired teacher, a beautiful house. However, the adjective for example cannot be used attributively when it refers to health. The meaning then changes to: bad or evil as in: ill health (bad health). makes up for this deficiency as an attribute: . Even when nominalized we still say: "the sick" and not "the ill". - but not .
Some adjectives are used predicatively especially after verb to be: the teacher is retired. The man is ill (sick) including BE and AmE differences. Some adjectives can be used in both ways.
When a past participle is used after "to be" i.e. predicatively it is still active at least in meaning. The verb "to be" here is a link verb which can only take an adjective unlike action verbs which take adverbs. Some verbs can be used as link or action verbs depending upon their meaning: She looks happy (link verb = appear + adjective: present simple like stative verbs). She is looking happily at me (action verb = with her eyes + adverb : Hence present continuous as with dynamic verbs). He turned quick (link verb: become + adjective). He turned quickly (action verb = move around + adverb).
Sometimes if you change the position of the past participle i.e. uses them attributively or predicatively the meaning changes accordingly as with and : The man is concerned (predicative: worried). The concerned applicants (attributive: involved). Those who are concerned - can be ambiguous in meaning. If past participles are used predicatively other prepositions (like: of, about, with) than by (which introduces the agent of an action) are used because they refer to states and not to actions: She was annoyed by you (action). She was annoyed with you (state) compare also: excited by vs. excited about.
The grey line here is very delicate but it shows that participles are a blend of verb and adjective and Germanic in origin. A language like English is thoroughly and heavily blended (a crazy German / Romance wedding) and anything which is soaked or blended to the bones is indeed a puzzle.