I never planned to get married and have kids. Actually, there was a stretch of time in my early 20s or so, where I was certain that I
never wanted to get married or have kids. (My uncle likes to pick on me about that occasionally.

)
Here I am now though...33 and happily married w/2 toddlers. Guess it all worked out in the end. However, I know that I would be perfectly happy right now if it had never happened. (I'm glad it did happen, of course...just saying that in some parallel universe where I never met my husband, I'm sure I'm happily sitting on a beach drinking margaritas.)
One thing I never did was set some sort of deadline for myself (If I'm not married by X age...). I had a guy friend who had his whole life planned out in very specific detail...he was going to play the field during college, work for a few years, meet the perfect woman, get married at 27, have a kid or two by age 30, etc. We used to laugh at him and remind him that he didn't necessarily have much control over whether he met the perfect girl at the right time. (And, of course, we sadly watched him pass up a few great prospects in college b/c meeting the right girl wasn't on his schedule until about 25 or so.

)
He did meet a girl at 25. She was totally not right for him. But, I think he tried for awhile to turn the relationship into something it wasn't, b/c it fit according to his timetable. Thankfully, she dumped him eventually...I don't think he would have dumped her otherwise, so he could have ended up in an unhappy marriage. He was really hard on himself for awhile about not living up to his own expectations, but it all worked out in the end...he met a great woman, got married at 31, and they have a wonderful son now.
You just have to take things as they come - if you settle b/c you're not married by a certain age, you might miss out on a great partner who you could have met had you held out another year or two (or five) before taking yourself off the market.