At 12 weeks the sex should be determined fairly easily. If a male, the testicles should descend within the next month. However, an absence of testicles does mean bunny is female. Sometimes one or both testicles don’t descend on schedule or at all.
A vet check is probably your best bet. Not a bad idea to have a health check done now before desexing age.

Your last rabbit lived to be 11 so you must have been doing something right! I have a friend who had rabbits growing up. They ate grass in the garden and table scraps. She’s mortified about their care compared to her current bunnies yet every one of them lived to be 13.

A lot of what you’re reading about care now really become popular in the last decade. Especially with rabbits becoming more common house pets and the establishment of The House Rabbit Society. There’s so much more resources on care available now. More product lines. More studies done on rabbit health. More information from sources other then rabbit breeders. Much of the info in the past was based on raising livestock.

I wouldn’t be surprised if in 10-15 years some of the advice given today in standard care will be tossed out for a new way.

On neutering, it’s not vital that male rabbits be done if they’re a single rabbit. (Again, 13+ years ago it was probably not promoted much. Nor there as many vets that operated in rabbits like there are now).
With female rabbits, there is a health risk leaving them intact. They have a high chance of developing uterine cancer at an young age.

Welcome here.

Lots of us made mistakes with our first rabbits, mostly because we just didn’t know better. It sounds like your boy was incredibly loved, you did the best you could with the info you had, and he lived a long life. Don’t beat yourself up about that. Focus on your new guy/gal. Giving him/her the best life ever will be a wonderful memorial to your first rabbit.

Welcome!!

I ditto-we all made mistakes with our first rabbits. Proper rabbit care (hay, big enclosures with out time etc), good veterinary care and medications are really just coming to the forefront now. Even now there are still products-foods, treats, cages which are so inappropriate/dangerous for rabbits sold in most major pet stores. (But promising that proper healthy rabbit items are also seeing shelf space!!)

It’s best to scope out a rabbit vet as soon as you can, and then you can verify sex, have an exam, discuss spay/neuter. It’s definitely not something you do just for behaviour; it’s for health as well as well being.

If you are beating yourself up too much, don’t think of it as you made mistakes or failed. Since that was the practice of the time and nobody knew better, think of it more as you are just improving your rabbit knowledge. And I agree with jerseygirl, we don’t know if the practices we do now will hold up to the tests of time either! I have had rabbits since I was 3 and members on here argue that my parents and I have done everything wrong every step of the way. Yes, my rabbits were in an outdoor hutch (heated during the odd cold winter here) until I was 13 because house bunnies didn’t really exist. And after that I never neutered my male rabbits until a couple of months ago (never had behavioural issues with any of them).

The trick to having a house bunny is to do your research (and that means looking at sites beyond just this one) and figure out what works in your home because there is more than one right way to keep house bunnies. Some people advocate that they must be completely cageless, but that isn’t possible for many people. People like myself confine them when I am away from home and let them have free run when I am home. Some will say that anything less than an x-pen is cruel, but other people build bunny condos instead. I live in the suburbs of one of the largest cities in Canada, but you would be amazed how difficult it is to find a rabbit savvy vet here! And my vet doesn’t advocate for “needlessly” neutering male rabbits if they don’t have behavioural issues or will not be housed with other rabbits. Talk to your vet and find out what they think is best.

And here is what I have the most fun with: research cage options!! It is amazing what is out there and what you can make yourself. You will find that you feel a lot less guilty those days you aren’t home to let him out if he has a large space to begin with!