You are NOT 20-something so please stop acting like you are.
Dress your age.
Wearing track pants outside of the house is not acceptable unless you are a phys ed teacher or something comparable. While we're at it, if you're a woman chances are your boobs are a bit saggy, and your ass is spreading. It's OKAY! Own it. But don't own it in a way that everyone else can see it. Yoga pants and tits hanging out shirts belong in the gym on 25 yr old girls who are built like brick shit houses...not 40 year old mother's of 3 (unless you are built like a brick shit house still!) Modesty is a hell of a lot sexier than you think.
You've probably got some wrinkles and grey hair. That's okay too.
Dye your hair, use some wrinkle cream but for God's sake don't put your make up on with a trowel. It looks bad. Less is more.
Don't use 20 year old street slang.
You've had 40 years to master the language and while some slang might be acceptable, being an educated person and talking like you're from da hood just sounds plain ignorant.
Flirting is fun.
We should all do it. But flirt with someone your own age because no one likes a cougar. It makes you look pathetic.
Embrace your age.
Wear it like a badge of honour. It's a hell of an accomplishment to make it to 40 and guess what - you're still young enough to have a lot of fun - but you're also old enough to know that going to bed at 11 pm on a work night just makes good sense.
Enjoy being 40.
One day you'll be 60. You'll move slower. Things will hurt more. You'll think 40 year olds are nimrods and 20 year olds are just plain idiots. Don't waste the best years of your life wishing they were a different time because one day you'll come to realize that being 40 is a hell of a lot more fun than being 20 was but by then you'll have missed it.
Live for now. Not for yesterday.