Let me preface this by saying I'm 25 years old and also contemplating TTC. So I understand where you're coming from. I've been thinking about starting a family for the past 5 years (ever since I met my now DH).
However, your post sounds a bit immature to me:
23 next June - as a pp said, it makes you sound like "I'm 15, but nearly 16"
3 next year - well, of course... you add one year onto a time frame, and naturally it increases...
I feel my purpose on this earth is to be a mother - this is not a healthy mindset. You have plenty of purposes beyond being a mother. Many women who want to be mothers never get the opportunity, due to infertility or other life circumstances. And those who do manage with this sort of mindset, put too much pressure on 'being a mother' which may negatively impact upon their children. Find meaning in your life being yourself as an individual, rather than yourself in relation to others. Once you accomplish this, I think you will be a better partner and mother (my mother focussed too much on 'mothering' and not on herself, which had some serious knock-on effects on her children and marital relationship).
I also want to be the first child to give my parents a grandchild which makes me feel like there is a clock on me as my fiancé’s parents already have a few grandkids and I want to give the first grandchild to one half of the family at least. I have good chances I mean my older brother does not want children whatsoever and my 2 other siblings are considerably younger and in primary school - this is just plain immature and a terrible reason to have a child.
I have set myself certain goals before having children, to ensure that I'm mentally and physically prepared to have them. I've spent my time:
- reading up on parenting resources,
- completing professional qualifications that I may not have time for once I have young DC,
- establishing my career, so that I have a good Maternity Leave package and good prospects for returning to the workplace
- establishing better lifestyle and eating habits, so that I can look after my children properly
- saving money for a home (I understand you have bought one already, which is amazing!!)
- creating a good social network (one that will be able to support me once I have a child, and isn't overly concerned with drinking and nights out)
- travelling to places that I otherwise could not otherwise travel to/may not enjoy as much with young kids (e.g. Zika virus zones, adventure holidays etc.)
I changed a lot over the past 3 years (for the better - I matured a lot!). I though I was fully adult at 22, but I can assure you that for most people this is not the case.
Don't put too much emphasis on 'getting pregnant before 25', 'having the first grandchild' etc. Establish who you are as a person first, take the opportunity to live a happy and selfish lifestyle in your early 20s (while you can - once you're a mum you'll have to consider your DC first in every decision).
And I would heavily advise you get married before you have children, especially since you are the lower earner - you need to protect yourself financially. You have only known your partner for 2 years. I've known mine for 5 and every year I feel I get to know the real 'him' more. From what I've read, partners can change a lot after children and you may be blindsided by your partner (i.e. he may end up being extremely self-centred and not help with child-care/sharing financial resources despite seeming generous at present).
Take some time to carefully decide whether you have adequately matured before taking this step. Best of luck, OP.