I hope that your big bash goes better than my 'landmark' birthdays always seem to have gone, Bobbi.
On my 18th birthday my dad had a darts match to go to. (He was the team captain). I didn't mind because I enjoyed joining him in the pub to play darts and, even though I wasn't a registered member of the team, I always got a game (covering for an inevitable absentee in the side) whenever he had a league match to go to. As it turned out, that was the only time that every single member of the team turned up, so I didn't get a game and simply sat all night in a corner on my own, supping my pint :(
My 21st birthday was on the day that we students returned to college after the Easter break. As a got onto the train, my mum gave me a load of cash and told me to have a really good celebration that night. When I got back to college though, all of my mates had either got back so much earlier that they were too pished to go out again or weren't due back until after the pubs closed. I found one guy, who I didn't really get on with, who allowed me to buy him a drink in the bar before saying that he'd have to go. Other than that, I was on my own all night :(
On my 30th birthday, I was joined by loads of teaching colleagues in a pub, many of whom kept buying me whiskies, even though I was drinking pints of beer. So I poured all of the whiskies into a half pint glass, to have as my last drink of the night. However, even though it was well before drinking up time, the barmaid cleared my glass with the empties and poured it all down the sink!
I can't remember my 40th birthday but I think that I was probably too hard up to be able to enjoy it much. I probably had a quiet night round at my dad's house.
I was working on my 60th birthday, asking people lots of silly questions on a footpath in Norwich. It should have been a late finish but I persuaded a colleague to cover for me, so that I could slip away early, actually managing to have a couple of pints with a mate that night. It was hardly a 'celebration' in the proper sense but at least I got out of the house.
The only 'big' birthday I've really enjoyed was a lovely night in a Moroccan restaurant with a couple of friends on my 50th, eating loads of good food, drinking far too much booze and stuffing money into the belly dancer's waistband ;-)
So I hope that you have more luck than me in the celebrations department!