Post Graduate Years... not after college, after high school
For whatever reason, your senior year did not go... well... enough.
Perhaps it went well: everything was hitting on all cylinders, but you need more time with a specialty before you move on up to 'the big leagues.' This is a common occurance for athletes and other performance artists such as musicians or dancers. Often they just need, or feel they need, more physical maturity and/or training before attempting to compete at the next level.
If such 'developmental' needs are the only ones that need be satisfied then there are some particularized academies such as IMG (https://www.imgacademy.com/) for sports or SCOPA (http://www.socapa.org) for the arts.
If, however, there are other and additional needs to be addressed such as academic enrichment and/or remediation, then perhaps one should consider a fifth year at a prep-school, one that indeed offers chances to develop one's particular skill but also provides the opportunity to grow socially and academically as well.
Finding a good prep-school that offers PG years is somewhat... challenging...: there are a number that 'offer' which you do not want to attend as they are weak schools just looking for another reveue stream, and there are some very strong schools that purport not to offer such programs but informally actually do, especially abroad and on the East Coast. Here is a place to start...but only to start: (http://www.boardingschoolreview.com/pg_boarding_schools.php)
I hesitate to say this, but this is one area in 'after HS/beforeCollege' that you will need---not just want but need---expert help.
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