I was older than you when I fell pregnant with my daughter (23), but it was still heavy going telling my parents.
I didn't live at home- I had just moved in with my partner (baby's dad) 2 weeks before I found out- luckily, mum and dad had actually met him, and thought he was nice.
I ended up telling my mum over the phone- which probably seems like not the best way, but it worked for me for a few reasons-
i had already decided I was going to have the baby, and I was determined to be positive about it, even though it was completely unexpected and unplanned, I thought if I told my mum in a way where she had the space to react to the news in whatever way she was going to, she could be free to do so without worrying about how it would make me feel. She cvould then tell my dad, and they could work through their reaction together, and get their heads around the information calmly and in their own time.
It's a big piece of news, you have to allow it to be absorbed before you can even begin to think clearly about it.
After a few days, mum called back to say she'd absorbed it, she had come to terms with the fact that this was the news of her first grandchild being on it's way, and although it was a bit sooner than expected, it was still the same news, and she wasn't going to waste a moment of it wishing it wasn't happening. She never wanted to look at her grandchild and know that she ever thought for a second that she didn't want her(or him) to be here. She said dad was still absorbing the news, and she was giving him space to do so.
My dad called a day later to say congratulations.
My daughter is now more than 2 and a half. I am 37 weeks pregnant with her little sister, and married to their father. We have moved around the corner from my parents, who couldn't be happier with my husband and family, and don't know how they'd ever cope with things being any other way. They are obsesed with their little grandaughter. This time 'round, I broke the news in person to my mum, and she cried with joy.
If you are going to keep the baby, I recommend providing your mum with the information- bare facts, and what you are planning to do. Then give her space to deal with it.
Even if you have to write her a note, and slip away for a couple of days. You don't want to have a big emoptional argument about it, and if your mum has some time to go through her reactions and emotions, without you reacting to her reaction, hopefully, it will be a calmer scene.
Best iof luck with everything.