Well Duh! *L* I should have figured out the age of the bike by your name huh!
But, given the fact that they are also 8 year old tires then yeah you probably do need to start thinking about replacements.
Actually they look pretty good with only the one crack. I'd give the sidewalls a real good check too since that is where the age stress seems to show up more.
Found this about sidewalls, it mentions Ford but gives a pretty general rule to go by
Over time, rubber degrades. Ford has recommended that tires be replaced when they are 6 years old to prevent sudden failure, even if the tire looks undamaged. In tropical climates, such as in Singapore, tires degrade sooner than in temperate climates. Tires on seldom-used trailers are at the greatest risk of age-failure but some tires are built to withstand idleness. This is usually done by using nylon reinforcement. In the past rayon was used in tires but it ages quite badly.
Patriot Guard Rider
2000 VN750 Sere (Serendipity)
1990 GL1500 (Ole Blue)
1986 VN750 EVie (project bike, heavy custom)
VROC # 11628 / 25000-H
ARVROC # 12 Coordinator and Crowd Control
OKVROC # 18 (H)
TNVROC # 45 (H)