Beth, you CAN put off all sorts of things that you've obviously considered doing-you mention travel for instance-but why would you want to?
The reason people say 'live your life first' is because once you have children they come first forever. You can't just abandon everything and hop on a flight to somewhere exotic, or go to the club with your friends on an impromptu basis, or stay in bed with take-away and your husband/partner all day because you feel like it because you have to plan, get sitters and get up for the children.
There's another old saying and it's 'youth is wasted on the young'.
The reason people say this is because when you're young you're reaching for responsibility and maturity and as you get older you realise that when you were at you're fittest, most energetic and fancy free you wasted it trying to get old.
I waited until I was 28 to have my first child. I went to university, all night clubs, foreign holidays, impromtu parties after a midnight phone call, travelled around as a sales manager, I did all that first. Now I've had another 3 kids and I'm a stay at home Mum and I'm 38.
But I'm enjoying it-I don't want to go out partying in a ridiculously loud club until 3am, I'm too old and besides, I've done it.
I'd love to jet off to somewhere hot and fabulous at a moments notice,(well who wouldn't?), but I can't & it's not a problem because I've done it.
What I'm trying to say is that you're clearly still young-there's lots of time to have babies and responsibilty-yes, children ARE marvellous but they tie you down (in a nice way) and they change your whole perception of life. Sky-diving doesn't seem so attractive when you're worried about what the kids would do without you and backpacking around Europe/Asia the World in general isn't much fun with kids in tow-hell, read the parenting page-there's times that going to the supermarket's not much fun with kids in tow!
Whether you like it or not as you get older your priorities will change. What you perceive as fun now won't be so attractive at 35 or 40.
Take the time for you and your partner to do things together, quality things, exciting, vivacious, young things so that you can take the memories of them into your older age and then regail your offspring with them in the future.
Nothing quite like being the Mom that's done pretty much everything ;)