for future reference, bucks can still impregnate for a few weeks (I think it could be 4?) after neutering as semen can live outside the testicles. so you'll want to keep him apart for at least those four weeks.
in older rabbits the recommended time apart after neutering is 6-8 weeks to allow hormones to cool down. after neutering hormones shoot upwards so bonding an extra hormonal rabbit can be quite difficult. given he's so young its probably not as much of an issue, the main issue will be the fact that he will still be fertile for a little while
preitler is right - smaller breeds do mature faster. generally I think the advised rule is usually 12 weeks old, but its more of a guideline I think and not a hard fast rule that they can't have babies until 12 weeks. I have heard of some rabbits supposedly being pregnant around 11 weeks or so, but it really depends.
I may be wrong but I do not think teats are a sign of pregnancy, I know Luna has them and she's never had a litter (as far as I am aware). most sources seem to suggest they're not.
best you can do is be on pregnancy watch as an in case, rabbits are pregnant for 30-33 days iirc. a few days (sometimes hours) before giving birth they'll pull fur out of their dewlap to make a nest. usually this means babies are due anytime now as they don't make a nest weeks in advance usually. provide extra food and a safe place to nest.
you may also need to separate the two does from one another if one/both are pregnant. I believe its recommended to give both does their own cage to raise their own litter over housing them together.