If you can afford it and your kid genuinely wants to do it, do it. But better to save money for when coaches will actually be watching your kid play for recruiting purposes.
They may watch the 26s to start a general look at the age group, but not as intensely as the 25s. If they watch 27s and 28s it is more for fun and because they are just there. A lot can change in the next 2-3 years for 27s and 28s: players quit, players have a growth spurt and struggle, players have a growth spurt and start to dominate more, etc. The vast majority haven't touched high school lacrosse, which is typically where you see a big change for a lot of players. | 
