In this YouTube video at 1:07 the person on the right says:
I've had some desperate moments when I've done that as a youngster.
Considering he's far from being a youngster right now, doesn't the as a youngster imply he's considering a past period of time not connected with the present moment, and hence the present perfect tense cannot be used?
What he says is
I've had some desperate moments when I've done that (slight pause) as a youngster, like I'm so nervous, I don't want to get...
The first sentence up to the slight pause has two present perfects, used correctly, to refer to the speaker's present state.
Then there is the slightest pause when his brain switches gears and he begins to talk about what he did as a youngster. He does this in the present tense, by the way.
The point is that at the pause, the speaker changes tenses in order to narrate a story about what he did or would do 'as a youngster.'
It is also possible that after he said the sentence with the two present perfects, he realizes that the last time he actually did this was as a youngster (not anytime recently), so he knows he needs to talk about the past.
But the perfect aspect is not used to narrate a story. So he has to choose between the present and the past to narrate (talk about) his own personal experience. Probably the fact he was first using present perfect to refer to the present helped him segue into the present, beginning with as a youngster. That he is speaking as a co-host of a live program probably also has something to do with choosing the present over the past to narrate his story. The present tense is more vivid. This is similar to using the present simple in headlines, when referring to a past event.
Notice he is using the simple past to narrate what the report says. This is perhaps to 'separate' what the report says from the rest of what the speakers say.
