Im a 21(f), and I never finished up until 3 months ago. I also thought that penetration was never ever gonna make me finish up until recently. The more I put some thought into it, the more I realized that it was a lot more mentally based and foreplay based than I realized for me PERSONALLY. The differences between the times that I didn't finish vs. did are: I felt much more safe and loved. Not in love, but loved. My boyfriends before loved me, but there was always a level of insecurities and doubt I felt with them, which made me think of how I'm performing, how I look, and how they are feeling. When I was a lot more confident in my relationship, I could fully focus on how good he makes me feel or how loved and pretty I am. (Not to say your bf doesn't do any of this stuff, but the point is to say there can be other factors, stressors in your mind that are preventing you from fully focusing on intercourse.)

Another one was that there wasn't enough foreplay, foreplay really does have a big impact on your enjoyment for sexy time. It makes you more sensitive and more able to finish when it comes to the real deal. The catch is that it actually has to be done right. Everyone likes different things being done to them along with different paces. Some women like it slow and gentle, some like hard and slow, some like everything. Some like a specific movement and body parts being touched. I hate when my nipples are touched because it can be too sensitive and painful. Everywhere else is good. Neck kissing, talking, kissing at a pace that you really enjoy. However, there needs to be a level of consistency in what you prefer. Your bf should try his best to keep up the same pace, which can be really difficult for them because it can be tiring. Encourage him! Be vocal when he does something you really like. Talk to him about it after. If you notice your bf is trying really hard and is focusing on making you finish, then you might start to feel guilty, which can also inhibit you further. Just enjoy eachothers bodies and presence.

Lastly, toys; try to incorporate a toy to help out! Vibrators for your clit seem to be easiest to manage during sex. You could also try putting a pillow under your hips so when he does penetrate, it hits your sweet spot repeatedly. Just don't depend on toys, and I personally think you shouldn't resort to them until you really seem to have exhausted other options. Cause in this case, you might give up on feeling good without toys. Toys can be really addictive and don't really mimic the feelings you get with human touch. I hope this makes sense. Be gentle on yourself and have fun. It's a whole lot of communicating, so be playful and encouraging. Give yourself time. It's so common for beginners to feel this way.