Why prefer older entry in BGP path selection only for eBGP neighbors?

[DA10]

I referred BGP path selection algorithm from below link

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

Can someone help to understand why Step #10 is only for external peers? Why is this rule not applicable for iBGP peers?

10.

When both paths are external, prefer the path that was received first (the oldest one).

This step minimizes route-flap because a newer path does not displace an older one, even if the newer path would 

[omz]

Why is this rule not applicable for iBGP peers?

When a BGP speaker receives an UPDATE message from an internal peer,
the receiving BGP speaker SHALL NOT re-distribute the routing
information contained in that UPDATE message to other internal peers
(unless the speaker acts as a BGP Route Reflector [RFC2796]).

Please also read this post - 

http://www.practicalnetworking.net/stand-alone/bgp-oldest-path/

[DA10]

@omz , Thanks but still the question remains unanswered..

I will explain with scenario.

Consider attached topology. Here R3 receives route 10.10.10.1/24 from R2 and R1.

Considering all criteria same, we reach step #10 of path selection criteria.

In this case, prefer oldest entry is not applicable at R3

So why is that, prefer oldest entry applicable to paths received from eBGP peers only?

[omz]

Does R1 receive route 10.10.10.1/24 from R2 and R3 only? Not from R4 also?

What does oldest entry is not applicable at R3 mean? R3 becomes unreachable?

R1 is receiving the route from R2 via iBGP or through R3? 

[DA10]

Sorry for confusion. I corrected the post. It is R3 receiving route from R1 and R2
R3 - R1 and R3- R2 are iBGP peers
R2 - R5 and R1 - R4 are eBGP peers
Now R3 has 2 paths, one via R1 and other via R2. In this case, why Step #10 is skipped?
Is there any limitation or use case where in step #10 is only used for eBGP only and not iBGP?