Forty Two is honestly not that uncommon, my husband and I are among the youngest parents (at 36 & 40) among my daughters year (Small rural school).There is a boy in my dd’s (8) class who has a brother who is only two years younger than me.
In your shoes, I would continue with the pregnancy. But then I will not/ could not/ will never consider a termination. My dh knew that from before we had sex together, that’s why we used double protection (condoms and pill) when we were not wanting to fall pregnant. After we finished our family, dh wouldn’t take the risk of contraceptive failure so he had the snip shortly after my youngest was born. Your h knew fine well that sex creates pregnancy (he has three beautiful examples already)! Every time you had sex he was playing Russian roulette yet he didn’t go for the snip.
Don’t let him blame you for this! If I were to guess, your h is having an affair and has been telling his Mistress that your marriage is sexless. I will be very surprised if he hasn’t been waiting for your inheritance to come through to divorce you and walk away with half. Now you are pregnant, if he tries to do you out of your inheritance, when everyone knows he has left you because he got you pregnant (and he wants nothing to do with the baby), then he will look like an absolute wanker/asshole and even his own family would be disgusted!
My advice is do what your heart wants, you have to live with this decision for the rest of your life! Your WH is leaving anyway, so don’t base your decision on his ultimatum. Terminating (like many believe about a baby), will not create a miracle cure/ be a sticking plaster for your marriage! So if you choose termination, let it be for your reasons not his! Your body, your choice!
At 42 you are still young, you can meet someone else, you won’t necessarily be a single Mum for the rest of your life!