It is a 12345 413 !
No 542135 is unattainable !
You can 135 anything you want and reach any destination in the world.
Just stay in a high 1342 and don't 42163 with the pessimists.
When I solved this to start, I made a few guesses for words which didn't work, until I guessed 12345 was some word like "great", and GREAT in fact is the right word.
Thus the two phrases are "It is a GREAT AGE!" and "No TARGET is unattainable!" I'll leave the others (6 is U) for other comments or to the reader.