Ok, we know that XIao Feng at age 30 is roughly equal to Murong Bo at age 60 or how-ever old he is in present-day DGSD. However, was Xiao Feng any better than Murong Bo at age 16?
We don't know of any feat performed by Xiao Feng at age 16; however, we do know that Murong Bo at age 15/16 was able to kill 24 year old Yellow Eyebrowed Monk in one stance.
Also keep in mind, up to that point Xiao Feng was just learning Shaolin techniques (most likely more internal-centric, which would later enable him to learn XL18Z). He hasn't learned XL18Z yet.
Furthermore, after age 16, Xiao Feng received martial arts instructions from Elder Xi of the Beggar's Union. This doesn't make 16 year old Xiao Feng look too hot, although it is true that an old-timer such as Elder Xi can still give some general pointers to a youngster who is much more powerful.
What I'm saying is, even though 30 year old Xiao Feng >> 30 year old Murong Bo, 14 years ago things could have looked different. Xiao Feng might have received a special boost at some point later due to one of his lucky encounters (it was said that he encountered many great lucks). It is possible for Murong Bo to have been better than Xiao Feng originally, but then Xiao Feng's rate of improvement sped up.