I know space marines cant reproduce as space marines, but can they have kids before they are recruited and start the process? Would make an interesting novel basis.

Well considering a lot of them were 12 when it happened, probably not.

My memory it's not very good but, in William King Space Wolves (1999), Ragnar go into intercouse with a girl after he completed his rites of passage.... or something like that.

Reference: http://www.blacklibrary.com/all-products/Space-Wolf.html

Depends on the planet. Some planets, like Krieg and Cadia, probably, because they are screwed up places. But generally no.

What in the name of the Emperor??
What kind of Slaanesh worshiping spawn of the warp...

Marines are usually taken as children, I assume some may be taken when they are older and some may have kids.
I don't know about after the imortification though, they may be able to, but it wouldn't be very romantic.

Ragnor had intercourse a few hours before he was nearly killed and selected by the wolf priest yes.

Captain Urial Ventris's great grandfather was also an ultramarine, he served in the 1st company and died fighting hive fleet behemoth.

Yeah, thats a quote you wont hear often. "I am a Space Marine, as was my father before me."

For example, the Wolves tend to take even grown men into the process of making someone an Astartes despite the increasing chance of failure, they may even had the chance to reproduce. But once they get into the Astartes buisness their mindset changes to some degree with their body aswell - and most of the things that mattered before becoming a Space Marine loose importance, family bonds for example. Also, even if one has a child, the kid wont get a free ticket to the SM train, and even generations can die by old age or just natural fighting before one going to chosen again from the same bloodline.

First, SM candidates have an age-range for the first implantation of their geneseed zygotes. In 40K it is usually 12/pre-adolescence to 16/18 year olds.
But in 30K they seem able to induct older candidates, maybe as old as mid-Twenties.

Some chapters seem to have retained some of this knowledge and are able to induct candidates who are teenagers.


But, there is an old short story called Deathwing where Dark Angels save their recruitment world split the survivors into new tribes and father members of those tribes, but their descendants were normal humans.

yes they have "normal" decendant: if we can consider normal someone that is a potential space marine neophite like the father.