My advice (as a mom of 3 kids, started at 30yo) is to enjoy your time now (if you're married and think/know you want kids 'someday'). Get your vacations and ski trips in now. Get to the movies now. If you're a reader, devour every novel now. Once you have kids, your time is pretty much gone. Sure, you get 'some' time, but nothing like you have now. When you have 3 - let's just say you 'give up' even trying lol (but I work FT, so I may have less time than others, don't want to completely scare you).
I always knew I wanted kids, but I really enjoyed my life in my 20s (married, house, no kids) - so much fun skiing with DH, hanging with friends, weekend trips, parties, being a Martha Stewart-wanna be. I wondered when I'd ever want to take the plunge. But then something clicked inside me. Suddenly, that wasn't 'enough'. Maybe it was age or something, but DH and I were ready.
You can't force it. It may come. Then you're ready for all the sacrifice and giving of yourself. Because man...you just give give give give...get much in return I tell you, but there are many many many days with little or negative return, but you just keep going and know that your hard work will (hopefully) payoff with a well-adjusted child that will be your ultimate legacy (and support you in your old age after the SS system has gone bankrupt and your 401k falls 99% - ha ha!).
This weekend I skied with my 3 kids and hubby - the littlest is 3yo and making turns and stopping on his own. Such a wonderful sight for me - all 5 of us together on the ski mountain (a first). It's these times when all the hard work and sacrifice are so worth it. Of course it was followed by my near-teen begging to get off the slopes (with eye roll), a 3yo tantrum and fighting over a cookie...