Five tables or a single table with an identifier column? Do I go with:
Multiple Tables Method
   table5up             table10up                 table15up                 table20up             table25up
[id   -   name] [id   -   name   -   age] [id   -   name   -   age] [id   -   name   -   age] [id   -   name ]
[1    -   jhon] [1    -   mike   -   14 ] [1    -   alex   -   17 ] [1    -   mark   -   22 ] [1    -   felix]

Or
Single Table Method
[id  -  name  -  age   - up ]
[1   -  john  -  NULL  - 5  ]
[1   -  mike  -  14    - 10 ]
[1   -  alex  -  17    - 15 ]
[1   -  mark  -  22    - 20 ]
[1   -  felix -  NULL  - 25 ]

Knowing that I may have NULL values, which scheme, using 5 separate queries for multiple scheme:
SELECT id, name FROM table5up
SELECT id, name, age FROM table10up
SELECT id, name, age FROM table15up
SELECT id, name, age FROM table20up
SELECT id, name FROM table25up

Or one query defined by up column value for single scheme:
SELECT id, name, age FROM tableups WHERE up &gt; 4 AND up &lt; 26

I will not call all tables all the time, only one per time as example for multiple tables:
SELECT id, name FROM table5up;

and for single-table:
SELECT id, name, age FROM tableups WHERE up = 5

Props:
id INT(11), name VARCHAR(48), age TINYINT(3)
Tables with the same structure but different sets of rows are sometimes called orthogonal tables. I don't believe in universal truths in the database world (which means: your use case could have peculiarities that I am not considering), but in general I consider orthogonal tables a bad idea.

From a theoretic perspective I can tell you that I especially don't like using metadata (table names) as data (age range). But what does it mean?

Tables designed in this way prevent you from running easily multi-table queries, like these:

SELECT AVG(age) FROM big_table;
SELECT up, COUNT(*) FROM big_table GROUP BY up;


Of course you will be able to obtain the same information with multiple queries, or with UNION. But it seems to me less clean and, should you ever need to add or remove a table, or change the usage of up (from 20,25,30 to 20,30,40), you'll need to make much more changes.

There are even more obvious case when the "one table" solution is better: maybe one day you'll need a query which returns people whose age is less than 23.

Flexible designs are usually better. For specific use cases, you can always create views, if really needed.