As the title says, are there any linguistic differences between accents acquired from birth/childhood and accents ued by adult language learners who speak the language fluently, but still with a pronounced accent? Can native speakers identify which accents are native and which are developed by adult learners?
An "accent", which is not a technical linguistic concept, generally refers to some deviation from a social norm, and unless you have e.g. the speech of the Queen as your guide, knowing exactly what constitutes that norm can be very difficult. In the context of American speech, "southern accents" are not the standard, nor are northern dialects (Chicago, Minnesota, Buffalo). Given that, I think your question has to come down to asking whether – given a target social standard of pronunciation – do people growing up in that environment acquiring that dialect as their first language pronounce things differently from adults who learn the same dialect as a native speaker?
Obviously in the case of L2 acquisition there is a vast continuum in how well L2 speakers acquire local norms of pronunciation, so you would want to only consider those speakers who have achieved very high phonetic fluency in the target language. I know a guy who migrated to the US from Israel as an adult, and he has an impeccable New York accent, to the point that other New Yorkers (not linguists) have commented on how he sounds just like a native speaker. I also know people who "have foreign accents" (Japanese, Spanish, Norwegian), but these are native-foreign accents, that is, they are the result of a local modification of pronunciation norms, arising from there being very many speakers of the dialect / foreign language and a high degree of bilingualism. Although most if not all second-generation Japanese are native speakers of English, their dialect is/was detectable.
I conclude that native speakers can make educated guesses as to whether a person is a native speaker vs. L2 speaker, but not always. If you are not familiar with the target dialect, your odds of guessing right are decreased.