So since the drama wont tell us and a couple of viewers here are confused (me included) about the ages of Dr. Gu and SWA, i did a little bit of math and research based on some info we gleaned from the episodes so far.
*cracks knuckles*
Dr. Gu said "Su Weian, class of 2012". Now usually this means people who graduated in 2012 or idk about China, but in a non-American context, this could mean people who started their degree in 2012 (as in the UK). I'm gonna go with the latter coz SWA graduating in 2012 would be way early.
i'm guessing the drama's events are happening in 2023 itself. So this means SWA met GYZ in his lectures during her MBBS. She would be about 18-19 years old when she started MBBS at Huaren since this is usually the university age for students in China. Then, SWA keeps saying "i only have a Bachelor's degree", which means she actually completed her MBBS and graduated. This would be in 2017 because an MBBS is a 5 years long course.
Then lets say she joined her Masters program (2-3 years long) where she meets Du Yuncheng, who is a "senior colleague" (as mentioned by SWA to her mom in a previous episode). Also, we know SWA was "abroad" for the last 3 years (as mentioned by DYC, Wen Ran, Muying and SWA's mom). Counting in reverse, it means she arrived in Lakaya in 2020 or late 2019. So, she was must have been in her 2nd year of Masters when that whole Wen Ran authorship thing happened and she dropped out without getting her Masters degree.
Finally, this indicates that SWA is currently 29 years old. We know she isn't 30 yet because she is dreading turning 30 due to the possibility of HD gene activation in her.
Moving on to Dr. Gu, lets say he followed the same study route as SWA. MBBS 5 years plus Masters 2 years and about 1 year of medical practice as a neurosurgeon. A total of 8 years starting at the age of 16 because i will assume he was a prodigy. So in the year 2012 when he was a guest faculty at Huaren, he was 24 (that's actually a believable age for younger faculties). Hence, currently he is 35 or 36 years old.
Also, if DYC is about 2 years older than Dr. Gu and he started the same study route with Dr. Gu in the same year, by the time DYC meets SWA during her Masters, he would definitely be her senior colleague in the university since he would be doing other research after his Masters had completed. SWA was probably working with him in the same project.
Update from ep 22: Dr. Gu is 32.............................................................