I am considering buying a used Harley Sportster. Is there a year model that I should avoid?

I would go for an '04 or later. The isolated engine really made it a much nicer motorcycle to ride. Before that, they vibrated so much they were pretty tough to use for anything but around town or fairly short trips. Post '04, they still vibrate like a HD at idle and around town, but as the revs increase, it smooths out. My 1200 Roadster was a great bike. It wasn't going to win any races against a Japanese sport bike, but it was still a fun motorcycle to ride. Unless you like to turn a wrench, avoid the older Ironheads. They are cool old motorcycles, but they need constant attention. I had one of the last XLX versions, and it just too unreliable to be practical.

Yeah every model, you're a pensioner, haven't you hit mid-life crisis yet? Guys like you in your saggy KC denims and corporate logos make me laugh. This is a young mans game granddad, buy a camper van with your pension or something / an RV

Yes avoid any Harley Davidson nearly all are plagued with problems. They are the most unreliable bike you can buy bar some Chinese or Asian brand bikes that no one in the west has heard of. If you want reliability and better performance and handling get a triumph cruiser or Yamaha or Suzuki cruiser.

Avoid anything from the late A.M.F. era, Sportster or otherwise.

2004 and later have rubber mounted engines. They are a LOT smoother than earlier models.

Get one with a side car you look like you should be a passenger in one.