Hello and thank you for your question.
There isn't much difference at your age to be able to know if she really loves you, versus a younger age. She would verbalize it and demonstrate it. Treat you with kindness and compassion, care about your needs and dreams, be there for you, make time for you, etc. Are these things happening?
This is Kristin...the expert who responded to your question at the beginning. I do think that this is "enough" to believe that she loves you. However, what is more important than what I think, is how it feels to you. If she is doing these things, that is putting love "into action" and it's not just talk. Other things to look for is that she is fairly consistent in her actions and feelings towards you, and that you she seems to enjoy your company, and care about your feelings, etc.
Other than this (combined with the things she is already doing and showing), you don't really need to look for more evidence. Simply believe what is happening in the present time. Otherwise, you risk not being present in the relationship, if you are always wondering and/or questioning her love for you.
Simply accept what she gives to you as it sounds quite good, and trust that it's real. There is no evidence (at all) that would suggest otherwise. Keep that in mind, when you start to have these doubts, that the evidence does indicate that yes, she cares about you and is sincere. Please click ACCEPT button, otherwise I'm not credited for my help. Thank you! Feel free to continue the discussion with me, even after clicking ACCEPT. Warm regards,