@MiniGuinness
Are people a bit dim? Because it is a weird way of wording it... if you are lucky enough. Although there were enough responses on this thread saying they love looking young enough to be thought of as under 25. Why? It’s not better, it could mean you have a big old moon face covered in acne, how is that lucky?
This. ^
I don't know why, but there seems to be this utter desperation from some people on here (and in real life too a bit,) to look/be thought of as much younger than they are. Like it makes them a better person, more special, and more appealing somehow.
And when someone says anything negative about it (like miniguinness up there,) they are accused of being immature, with comments like 'you must be very young.' 
Well I'm not very young, I am an old codger who won't see 45 again, and I find these comments laughable and ludicrous. I have seen SO many of them on here, and other forums, and heard so many in real life... People claiming that people think they look soooo young, and they are 43 and were asked for I.D. to buy a can of red bull!
A woman I work with (who is 45,) recently claimed that everyone mistakes her for her 20 y.o. son's sister or girlfriend, because she looks soooooooo young. 🙄 She looks every bit her age, even though she dyes her mousy hair black, and has botox injections. Oddly, I have never ever heard anyone say she looks young for her age!
I have no idea why some people (usually women) are so desperate for people to say/think they look younger than they are. WTF is so bad about looking your age FGS? 
I remember a woman (several years ago,) asking me to guess her age (you can tell when people think they look young for their age, coz they always ask you to guess,) and I thought she looked about 39-40. So I decided to be generous, and said '35-36.' She said, 'I am 35! Bloody cheek,' and looked really annoyed.
I was baffled, and I said 'what did I say wrong?' 'Well...' she retorted, 'everyone else thinks I'm in my 20s!' with a
kind of look. So the silly goose was pissed off that I guessed her age exactly. As I said, I was being generous and I thought she looked 40 anyway!
If the claims (from some) are true, that they are in their 40s and shop assistants are asking them for I.D. to buy booze/scratchcards/red bull etc, then all that proves is that the shop assistant has poor eyesight, or is absolutely shit at guessing people ages. (Or as @FishCanFly said, they are taking the piss...)