Conceptually, they're not the same, so mixing both is not a good idea on most cases. However, in your specific case, you could be a bit more generic. Take this for example:
There are problems.
Then you could list what the problems are and what to expect from user's input.
This being said, I think you're on the right track with the content of error messages. But you're also creating some huge cognitive overload. You have messages, colors, icons and bars. You should just focus on being clear and descriptive. And some minimalism wouldn't hurt at all. Quite honestly, I get dizzy and don't know where to look, everything is calling for my attention, which means NOTHING is calling my attention as expected.
On top of that, I think errors and warnings aren't correctly defined. If user's input is incorrect, then that's an error, not a warning. Thus, the easy way out for your form is... all of them are errors. Bam! You don't need to distinguish those pesky warnings, you can get rid of all those icons and colors and colored bars and stuff. Just focus on what matters: the user providing a correct input.
Something to note
See how I mentioned "they all are errors?". Well.... yes. But the user doesn't need to know that.
Instead of using the word error, you can be more positive. A good way is to use humor and blame the system instead of the user. Another way is to use a conversational approach and guide the user through the expected behavior (you have it quite right so far).
For example, instead of "The graduation year for this birth date is not within yadda yadda yadda", you could use something like "Are you sure? This date doesn't seem correct" or "Snap, I can't believe it took you 12 years to finish High School!" or something like that
One last note on IA
In terms of IA, are you sure you need all those fields? For example, do you REALLY need the birth date? If so, do you REALLY need the grade or graduation year?
For what I can see, you want to create teams based on age (absolute or relative). Unless there are very strong reasons to do it otherwise, you should use only one parameter: absolute age (based on birth date) or relative age (based on grade or graduation year). Once you define which one, then everything will be simpler. And of course, if you use teh graduation year approach,
active checkbox is not needed, the graduation year field will define that.