Early to mid 20's. Just got together with my, now, DH, and we didn't spend enough time together. We both had hobbies, spent (too much) time with family commitments, spent too much time on our respective professions. We basically just "fitted in" each other between everything else. What should have been "Our" special time getting to know each other, our "firsts" etc., were rushed. Rather than prioritising each other, we prioritised other things. We thought we'd have plenty of time for ourselves, but there was always something else/someone else needing our time. Not saying we didn't do things - we had lots of lovely holidays, but that we really our only "us" time, limited to 2 or 3 weeks per year - always stressful because of all the planning we had to do to keep other people happy whilst we were away.
It basically pushed everything back - married in our mid 30s, first (and only) child late 30s, then just as soon as we got our son to school and not needing us as much, we had serious illnesses in both our parents which again soaked up our "us" time. Then, sadly after their respective deaths, and our son went to Uni, we thought we'd have our "golden" years in retirement, but then DH diagnosed with incurable cancer. Thankfully still with us, but realistically, I'm looking at retirement on my own and pretty pissed off about it.
So we've never had our "us" time at all. Just one thing after another. I'd go back to our early 20's in a heartbeat and prioritise each other and do what we wanted to do, not do what everyone else wanted us to do to our detriment. Yes, I know it sounds selfish, but there has to be a balance between looking after other people and looking after yourself.