20 and want a baby

When I discuss this with people they think I am nuts for wanting a bad y so young. I have a stable job and I'm with a great guy. The reason I want a baby so bad is I know that our 20s are the best years for conceiving and so I don't want to waste precious time.. I may have screwed up and be pregnant this month as I wasn't as careful and I should have been but if I'm not I'm going on birth control the end of the month.. But am I crazy for wanting a baby young when fertility is highest?