Also, there is no specified 'girly' level that requires you to wear a dress. I would imagine any woman has the potential to wear one, if she chooses to, so maybe it's more about familiarity, and those weird rules we set ourselves early in life - we end up restricting our own choices for one reason or another.
I practically lived in babydoll and indie style dresses all of my life until about 3 yrs ago when i simply started to feel different. It felt like a new adventure to seek out new things, and I have been pleasantly surprised to find how other styles suit me, especially skirts and jeans. But that's just my personal experience.
One thing that stands out to me: why do you care what teens are wearing anyway? Do you really feel a desire to wear cut offs with tights? I think older people don't wear this combo because it isn't really practical (kids, work, actually wanting to be seen as more mature and taken seriously), not simple because they can't get away with it any more. To be honest, I think I would look good in them, my bodyhape and legs would suit them, but the thing is I don't actually desire to wear them, it just ain't my thing.
So i think a lot of women over 30 just tend to change naturally, not because there are hard and fast rules, or that their bodies are somehow 'lesser' than younger women. This is actually bullcrap, for not all young bodies are good, as not all older bodies are worse!
I think many people define 'safe' as something they resort to when they're not feeling too great about themselves. We all have those times, and that's okay. But seeking nicely fitting pieces which really suit you are not about safety - it's more to do with knowing your good parts and capitalising on them. it's about avoiding stuff that doesn't make you feel great.
And I don't wish to sound all cheesy or anything, but maybe if you made a list of the things you LIKE about your face and body, that would be a better place to start, and work from that. That internal dialogue goes a long way to determining how we present ourselves to the world. It makes or breaks our confidence. I generally feel good in most of my clothes (unless I have PMT!), but if I spent a lot of mental energy listing my physical flaws, I would never leave the house.
Sod convention, nobody is judging you unless you do something extreme, 30 is very young - and if it's not, then god help us all because that means nearly 50 yrs of the average lifespan is meaningless.