there are landmark birthday's throughout one's life and i think, based on your culture, they are pretty consistent and yet still debatable.
year 1 - this marks the first year of your life and although you don't necessarily remember, it is significant for those who love you. as jerry seinfeld notes that your first birthday and your last one in old age are quite similar. "your not quite sure whats going on," "other people have to gather your friends for you," consequently you are thinking, "these are my friends?" nonetheless this birthday is big for mom's especially.
year 5/6 - depending on when you start kindergarten. this is a landmark year because, i feel, you are understanding the greatness of friendships and sleep-overs (even though they usually end in the parent coming to get you in the middle of the night) and the outdoors. you start school and have lunches where you begin to understand the value of this event. a lunchable is the greatest thing to bring to school besides a surprise visit from your parents who may have brought mcdonalds with them. also, at this age you know and can appreciate the value of birthday's so its fun to be recognized in front of your friends.
year 12/13 - the next is the years that usher you into middle school. it is a stretch from 5/6 to 12/13 but that amount of time is necessary to prepare you for the most dramatic moments in your life at this time. even then, most are NOT prepared. things start changing and faces become all weird looking and somewhere in the mix you can throw braces in there. hair in weird places, smells, zits, incontrollable voice influx, it is a wonder how this is the moment that teens begin to really like and become attracted to the opposite sex. but these are the years to take notice of relationships and most do take advantage of the moment.
year 16 - ah yes, sweet 16. the year of freedom, so to speak. most get their license and are able to drive, unless you are poor and you have to take the home school edition in which your dad makes you read EACH page twice before he signs off on it, oh and at age 17 no less. i really had no issues with getting around because most of my friends at this point were 1-3 years older than me so transportation was not my biggest problem. most start high school or have in the last year and are now learning what it means to be at the bottom of the pack again as "fish" in a sea of sharks. these years for me where the greatest years of my life and even though i would like to go back and change things i still would love to just go back and experience them again.
year 18 - graduation is in your presence. you get to move onto a schedule that YOU choose, but you must choose wisely. at this time you must register to vote (even though i think they should raise the age requirement) and you will most likely vote for whoever lady gaga tells you to vote for. at this age if your into naughty things you don't have to ask random strangers to buy smokes for you (similar to 21 and alcohol) at gas stations. starting college is big too and becoming more popular. don't be fooled by a school that seems to be more of a party school than others...if there are college kids, parties will happen. most still don't know exactly what they want to pursue at this point of entry. even still, some will change their career choice and start something that they did not even get a degree in.
year 21 - graduating university and starting to look at the rest of your life is what is kind of taught within our culture. although i believe this trend is changing. at this age you are able to get into places that shun away the teeny bopper (i.e. bars and night spots) which may be due to the fact that in the united states you are capable to purchase something called "alcohol" (and many do). responsibility is now your friend or arch nemesis. in the years previous you have noticed it gaining strength and maybe you have been able to withstand invasion the time is now rapidly approaching when you will NOT be able to escape its grip on your life. responsibility will choke you out if you don't surrender to it.
year 30 - hopefully you have settled down a bit by now and are ready to help someone else with their life responsibilities. if not there is still time. most are finding out their passions and what they like to do as opposed to what they are forced to do. it can be a bit scary, depending on your perspective, at this moment. for me, i am not scared because i see the glass half full right now. there is a refreshing peace when one is able to reflect on their past and see the hand of god on their life. the longer the experience the greater the reflection and peace.
i will not go on here to the 40's or 50's and beyond. although i do think the next monumental years in one's life are every decade after 30's. when i reflect in greater measure over my life it is hard to not think of the initial circumstances (positive and negative). but i truly remember many events that have stuck with me, shaped me, and in some ways derailed me. these are memories i would not change. i do think about what life would be like 30's from now. it seems like it took so long to get to this point. i wonder if it will feel that way when i am 60. i do know this if i am doing the exact same thing: married to liz, emotionally connected with my sons, serving in ministry with close friends, studying god's word and journaling everything he is saying, looking forward to holidays with family, and living the life that reflects who god is, i know i will be deeply satisfied with his handiwork.