Things I know now I wish I'd known when I was 25...
Your body is young and beautiful and strong. Love it. Don't fret about it, but that body is going to visit all kinds of troubles upon you. Had you not been young and strong... well, you'd be chatting with Achilles trying to decide if the short and glorious life really had been all it was cracked up to be. It sees you through.
Dave is as good as he looks. You could give the guy a break and stop testing him every which way. But even if you don't stop (which I happen to know, you don't), he'll stick. You could do a little more to deserve him, I suppose.
Stop squandering your chances. It's the worst kind of waste. Put on your big girl pants and claim some of these opportunities.
Good things await you. A husband whose eyes sparkle when he's got a naughty idea. Beautiful healthy children who actually like you. Solid relationships with your multitudinous siblings, who are weirdly different from you and yet eerily similar.
There are things you get really good at. I know you think it won't happen, but it does. Your path takes a long time to unfold before you, but it does show up. It wouldn't hurt to pay a little more attention. The kids distract you, but that's more because you're afraid than because they need you. (Well, they do need you, and you turn out to be a good mother... but you also hide behind them. Knock it off.)
You know what? Spend more time on you. Stake a claim. Take up some space on the planet. And if you forget, or lack the courage at 25 (which I happen to know, you do) then do it as soon as you notice. Leave fear behind.
Now.... what would my 70 year old self write to my 48 year old self?????