I make it a point not to respond too harshly when women say this. You gotta look at it like this: a woman goes out with 99 guys, all of whom want to bed her/propose to her/express their feelings to her by the 2nd or 3rd date. So, her knee-jerk response to a guy taking her out is "I want to move slow." It's based solely on previous experiences where guys have wanted too much too soon.
However, I'm NOT that guy. Personally, I like taking things slow and getting to know them.... so I make it a point not to do the things most guys do that make them appear as though they're moving too fast. I don't call/text between dates except to ask them out; I wait a minimum of 4 days between dates before asking them out again; I don't push for sex on those first few dates, nor do I get all touchy/grabby before she does; I don't over-compliment her or tell her how much I adore her... THESE are the things that guys do that make a woman feel as though he's moving too fast.
And that's the key - you can't make her FEEL like it's too fast. However, if you're acting patient on those first couple of dates and doing the things I just said above, you can usually have a girl ready to sleep with you by date 2 or 3. Not that that's all you should be in it for - hopefully you actually want long-term relationships with these girls. But the point I'm making is, it's not about how LONG you're dating her before she makes you the boyfriend; it's about how fast she FEELS it's going. If you do the right stuff, you can technically have a girl begging to be your girlfriend in less than a month - but if you're doing the WRONG stuff, you could be dating her for 3 months and have her still thinking you need to slow things down. Hope this helps!