For the sake of just having these rules, they will be included. Like a wise man once said "Without rules, they'll go about killing, pillaging and impregnating my world" so, lets at least have rules for how that is done.
Unlike the older Fallout's, or the newer ones without the option, your character needs food and water... or at least something that is similar enough to it. (Ghouls do not need to feed, but can. Cyberponies also need power to stay functional)
Seeing how we all are adult here... or at least should be a bit into our teenage years, this topic shouldn't be so flabbergasting. After some consideration, I've decided to go with the following rules: Mares in this world will have "seasons". And no, before you go there: They do not become sex craving crazy mares in this period of time... well, maybe the raiders do, but that's beside the point here.They just get a slight desire to reproduce. The equivalence of ex: Seeing a piece of candy over there you kinda like. You don't need it, but it'd be nice to have it. To determine what age your character would be starting to get in her first heat. (aka: become sexually mature) And do note, this is only done if you aim to play younger then 16.
If so, then roll a d4 (+/- 1 if you or the GM feels like it) and add 9. This would put your character in the age span of 9-14. Male character roll the same mentioned but add 11, resulting in 11-16. However, I personally hope to Celestia that you will not have to use these rules... or plan to... In either case. A mare is in season for ~3 months. To determine which, roll a D12, and add 2. These 3 months will be it. The chance of pregnancy is the following: If in good condition and health. Make a hard roll against End, +15. If in somewhat rugged condition, not properly fed. Make a hard roll against End. If badly messed up and starving, Make a neigh impossible roll against End. For example, a healthy mare with 10 in End would have a 45 % chance in the first example, while a mare with 5 End would have a 15 % chance in the second example. And a mare with 1 End a 1 % chance in the last example. Magic, chems and "other" things can increase or reduce this chance as well. Or even remove it outright.
This is entirely up to a player to decide (or GM for NPC's). There are indeed traits that "makes" your character one way or another. But to not force someone to pick a trait, you can be this or that without it. It will however, not grant any bonuses for it. And if just lazy, or having hard to choose for a NPC or character. Roll a D12, then use the following: 1-2= Gay 3-6 = Bi 7-9 = Pan 10-11 = Hetro 12 = Asexual
A normal pony could expect to live around 90 years (+/- D10) depending on how healthy they lived. In some rare occasions, they can get even older then that. Stable dwellers in a stable could usually live up to that age, while in the wasteland, most would suffer -3D20 years due to radiation, hazards and malnourishments. Cyberponies and ghouls can expect to live for allot longer due to well... "augmentations". Cyberponies rely on technology to keep themselves alive. And ghouls simply just... "live". They however require a small dose or radiation to keep themselves "living. Robots can stay functional as long as they got power and haven't corroded. If they run out of energy, they could simply swap to a fresh source and keep on rolling. Assuming they'd have something to help them swap. (Also, pregnancy lasts ~11 months for ponies)