Obviously in the immediate term you cannot "make up lost time". All we can do is make the remaining time as good as possible.
On the positive side, you will have far greater self-awareness now. You'll know how your mind works and how not to over-strain it. These are important things over the duration of a doctoral programme.
You will also be aware of the need to balance life and work - however well work may be going or however frustrating it becomes.
What you have learned about life and yourself will be very useful over the next years. Apply it wisely and ignore the follies of your professional contemporaries but experiential juniors. It might be good to link up with some mature doctoral students in your department or around the campus generally (regardless of country of origin) as we all have an emotional connection with our own age group.
Focus on quality of work, not speed or quantity. Try to give a little back to the system you work in, time permitting - and in an even-handed way - to those around you.
In the long term the quality of our remaining life is what determines if our "lost" periods were truly lost or not.
It is very important to get rid of this "catch-up" mindset prior to starting a PhD. If you find it hard to shake off, especially even after some sessions with a therapist, I think it would be wiser not to go into the programme just yet. Maybe a 9-5 RA job for a while or something outside academia.
I say this because there will be younger researchers rushing around and maybe trying to generate a competitive dynamic to assuage their own doubts and anxieties. Sadly, there are always some faculty who cultivate competition between postgrads. You don't want to be part of this madness.
So you need to be clear and strongly firm - on bad days as well as good - on your quality of work and life mindset before taking on any serious research programme commitment. Please discuss all this with your therapist.
Also look your would-be supervisor in the eye as you tell him/her that work - however interesting and rewarding, however important success is for the department's appearance in the eyes of research grant givers - is not all there is to your life. In the situation you are in, a down-to-earth supervisor with an "ordinary" project would be far wiser than a pushy supervisor with an "exciting/topical/heavily-funded" project: you'll have more time for TA work, colleague engagement and learning by doing - all things that are vital for your development and self-confidence.