The Nimrod is essentially a Comet 4C with an unpressurised weapons bay added on underneath, creating a ‘double bubble’ effect that gives the aircraft its distinctive appearance. However, the original Comet was designed back in the late 1940’s and first flew on 27 Jul 49, so the basic Nimrod design that evolved from the Comet 4C owes more to the 1950’s than to any other period and, although this has had many advantages, it has also had some significant disadvantages. The Nimrod MR1 first flew on 23 May 67 and the aircraft eventually entered service with 236 OCU at RAF St Mawgan on 2 Oct 69 – the first of 46 aircraft eventually delivered to the RAF. From the late 1970’s to the mid 1980’s, 35 Nimrod’s were fitted with upgraded detection systems, including the EMI Searchwater radar, and were re-designated Nimrod MR2s.
35 of the original 48 MR1s became MR2 and then 21 were going to become MRA4 - that in the end would be 3 development and 9 production variants.
If you are meaning "age" as date of manufacture then you are correct (by 3 years out of a total of 44 years since 1967). But if we regard "age" as useage then in airframe life then the RJs are definately younger.
iRaven