pepper & VB.. i feel for you guys, even though my parents were an average age (20's/30's) when they had me... but remember that a lot of single children are going through a similar thing to what you've gone through... not only do they not have siblings, but they will never be an aunt or uncle... or have nieces & nephews, or brother or sisters in law (through a sibling). if they have a kid, their kid will never have aunts, uncles, or cousins (unless their partner has siblings). if they don't have or adopt kids, when they get older, & the older generation is gone, they will be totally alone (aside from whatever partner or friends might be in their life). believe me it's a very scary and lonely thought.
i know some mothers who had kids at 40, and it was definitely a major dilemma for them... but as for being selfish, you might as well say that every person who gave birth on planet earth did so because they were selfish. remember that also very young parents have kids for selfish reasons, and are often not even properly equipped- mentally, financially, etc. sometimes an older parent can make up for a lot in wisdom, stability, ability to focus on parenthood.. that they didn't have in their youth... just something to think about.
there's a lot of children who experience emotional neglect by average-age parents who are workaholics, having marriage troubles, or just couldn't give it their all for whatever reason.. (but what's their excuse? they can't say old age.) so you're not alone!
anyway.. for those us lacking in a surplus of extended family... that's even more reason to make sure you always have a lot of good friends and social contacts.. and you can always have a surrogate, for a family member you missed having in your life.