My partner wants kids!!

Ladies I really need your help, me and my partner have been together for 2 years and I love him with my whole heart, we have spoke about kids before ( at the very start of our relationship and again about 6 months ago when we decided to move in together) and we both want them, there is quite a large age gap between us and it had never been an issue, until yesterday, when we discussed kids I had told him I wasn’t ready and wanted to wait until I was settled in a steady career and we were financially stable (we are both financially stable and in decent paid careers but mine is still fairly new and taking off) we have only just moved in together 2 months ago we are still getting used to living in each others space and it’s been amazing so far, we were at my friends wedding over the weekend and her little boy was there he’s 3 and soo adorable, we got home yesterday and my partner tells me he wants us to start trying for a family of our own, all my brain could think was I’m not ready, I love kids and I love him but I’m not ready, I was honest and told him how I felt and he brought up that he’s older and how most men his age have a family by now, and now things feel strained between us, I love him so much and do want children with him, but not yet. Am I being selfish by saying this? and how can we fix the strain between us now?