Thank you guys for your input guys!
@SilverMonocerosStud We are making some changes as to what is needed to get to the next levels to encourage players to delve more into their characters and hopefully interact more with other players. The XP amounts required as they are now will remain the same, we are just adding in new requirements on top and some of those may be time frame sensitive, hence the question.
For example in the breeder career, some requirements will be to breed your own horses, but also to offer up a stallion for stud.
There will also be a requirement to use someone else's stallion for a breeding at some levels.
Of course all those activities (or almost all) will gain you XP as you do them.
We are adding quite a few new ways to earn XP overall.