how old is too old when buying speakers?

Aside from abuse, THE part of concern is/are the capacitors in the crosover. They, reportedly, have a ten year life.
Peace-on-Earth

Trust your instincts...if it seems too good to be true...or u sense the seller maybe playin' ya...pass...there are too many reliable folk on Audiogon...always check feedback,call seller,have pics emailed,etc...this doesnt guaranteee a smooth transaction...but it sure helps...just for the record...I tend to go with dealers over individuals...also...in a small room the Tukans would be fine...

I've bought lots of stuff on a'gon and have not had any problems with the transaction. (Fedex is another matter).

I've bought two pair of Tukans for secondary systems and think they are great for the cost.

Assuming they weren't over driven, 10 years is conservative and yes the capacitors will go first,

speakers that have a good quality cabinets can never get old.
drivers are replacable even on some of them you can replace just a voice coil on older models if the driver surface is still stiff.
thiels are probably the oldest descent speakers out there that are OK for used.
kefs might not be as good...

I bought a 10 year old pair of Spendor SP1's. Excellent speakers still.