http://en.wikipedia.org/wiki/5000_metresIn 1987 the world record was 12:58 and it was at 13:00 in 1982, so you could argue by some peoples logic on here that Kennedy should have been much faster than that in his prime years later (i'm not saying that).
However the record was 12:44 in 1995, and 12:39 by 1997, the years you list as his prime. Incidentally Komen also ran 12:45 in 1996.
Best year performance
[edit] Men's seasons best (outdoor track)
YEAR TIME ATHLETE PLACE
1960 13:38.1 Pyotr Bolotnikov (URS) Kiev
1961 13:38.2 Murray Halberg (NZL) Stockholm
1962 13:38.4 Murray Halberg (NZL) Auckland
1963 13:38.6 Pyotr Bolotnikov (URS) Zürich
1964 13:38.0 Bob Schul (USA) Compton
1965 13:24.2 Kipchoge Keino (KEN) Auckland
1966 13:16.6 Ron Clarke (AUS) Stockholm
1967 13:18.8 Ron Clarke (AUS) Stockholm
1968 13:27.66 Ron Clarke (AUS) London
1969 13:29.0 Dick Taylor (GBR) London
1970 13:22.8 Ian Stewart (GBR) Edinburgh
1971 13:22.2 Dave Bedford (GBR) Edinburgh
1972 13:13.0 Emiel Puttemans (BEL) Brussels
1973 13:14.51 Emiel Puttemans (BEL) Stockholm
1974 13:14.4 Ben Jipcho (KEN) Christchurch
1975 13:18.6 Emiel Puttemans (BEL) Papendal
1976 13:13.10 Dick Quax (NZL) Stockholm
1977 13:12.86 Dick Quax (NZL) Stockholm
1978 13:08.4 Henry Rono (KEN) Berkeley
1979 13:12.29 Suleiman Nyambui (TAN) Stockholm
1980 13:16.38 Miruts Yifter (ETH) Bratislava
1981 13:06.20 Henry Rono (KEN) Knarvik
1982 13:00.41 David Moorcroft (GBR) Oslo
1983 13:08.54 Fernando Mamede (POR) Tokyo
1984 13:04.78 Saïd Aouita (MAR) Florence
1985 13:00.40 Saïd Aouita (MAR) Oslo
1986 13:00.86 Saïd Aouita (MAR) La Coruña
1987 12:58.39 Saïd Aouita (MAR) Rome
1988 13:11.70 John Ngugi (KEN) Seoul
1989 13:04.24 Yobes Ondieki (KEN) Oslo
1990 13:05.59 Salvatore Antibo (ITA) Bologna
1991 13:01.82 Yobes Ondieki (KEN) Zürich
1992 13:00.93 Moses Kiptanui (KEN) Brussels
1993 13:02.75 Ismael Kirui (KEN) Stuttgart
1994 12:56.96 Haile Gebrselassie (ETH) Hengelo
1995 12:44.39 Haile Gebrselassie (ETH) Zürich
1996 12:45.09 Daniel Komen (KEN) Zürich
1997 12:39.74 Daniel Komen (KEN) Brussels
1998 12:39.36 Haile Gebrselassie (ETH) Helsinki
1999 12:49.64 Haile Gebrselassie (ETH) Zürich
2000 12:49.28 Brahim Lahlafi (MAR) Brussels
2001 12:56.72 Richard Limo (KEN) Zürich
2002 12:55.85 Salah Hissou (MAR) Rome
2003 12:48.81 Stephen Cherono (KEN) Ostrava
2004 12:37.35 Kenenisa Bekele (ETH) Hengelo
2005 12:40.18 Kenenisa Bekele (ETH) Paris
2006 12:48.09 Kenenisa Bekele (ETH) Brussels
2007 12:49.53 Kenenisa Bekele (ETH) Zaragoza
2008 12:50.18 Kenenisa Bekele (ETH) Zürich
2009 12:52.32 Kenenisa Bekele (ETH) Zürich