This is an old question, but I want to make a point clear:
Yes, the present perfect is used all the time, by native English speakers, in all registers and dialects of English, from extremely informal to very formal. You cannot sound like a native English speaker without using it when it is called for. (It's not like, say, knowing how to use "whom," which you don't really have to do.)
The good news is that, in a lot of places, the two are interchangeable. Moreover, you are likely to use the past more. Also, using the present perfect in the wrong place will sound very strange and sometimes make you unintelligible, whereas using the past in the wrong place may communicate the wrong shade of meaning but will rarely get your listener completely lost. Therefore, I recommend using the past most of the time, then inserting the perfect gradually if you are sure you are right.
To make sure I wasn't wrong, I turned on the TV now to a sitcom rerun. Ignoring other tenses (mostly present) here is my tally in ten minutes or so:
past 31
present perfect 4
and some other past tense constructions:
"lately, I have been having thoughts"
"I think that may have missed the table."
"oh God, I shouldn't have said anything"
"he kept laughing at..."
You should use the appropriate tense at each point. You start talking about the summer in the past tense. No problem here.
This summer was horrible, I didn't even get to go anywhere.
Next you change to the present perfect. That's not an error. But the use of the word struggling is awkward, it looks like translationese. Better to use past tense for the accident and present perfect for your current state:
My brother had an accident, and we've been helping him recover.
"B" can also use whatever tense is appropriate. First sentence is about the past, so past tense. Second sentence is about the present, so present tense. The "I'm loving" is casual (continuous tense of stative verb), but I think acceptable here
We did loads of things and I had lots of fun. Like now, for example, I'm in New York! I'm loving everything about it.
A sentence can have mixed tense:
Yesterday I went shopping, as I will go to a party tomorrow and the bag that I had bought to take with me was too small.
Each finite clause has its own tense, and while jumping around tenses too much is confusing for the reader, and bad style, it is not incorrect.
Best Answer
The present perfect is useful to ask questions where there is a connection between the event in the past and the current state.
In this case you can understand that the first two questions are asking "Is your dress sense now, different to how it was in the past?" The connection to the present is clear.
But the last question introduces the phrase "In your 30s, 40s..." That places the question as a question about a particular time in the past. So the past tense is natural.
Compare with this dialogue:
The first question is really "Are you hungry now", and the connection to the present makes "have you eaten" natural, even though the phrase "recently" refers to a past time. The second question is about the past. Tense is chosen appropriately.
Similarly "in later life" keeps the connection to the present. Whereas "in your 30s" makes it a question about the past.