is there way to deposit longer than 12months?
This is possible but not recommended. You should deposit for 12 months and on maturation block then re-deposit
EDIT: Dev explained this earlier:
is there way to deposit longer than 12months?
I would like to deposit some coins to 15 years if possible

The wallet will let you deposit for more than one year but please don't do that because you will lose money. After one year there is no payout on locked coins. This means if you term deposit coins for more than one year you will be locking up the coins for no ROI and I don't recommend that.
Correct. Interest is coded to only pay a year, 12 months, 52 weeks (or actually equivalent blocks at a guesstimated 720 blocks per day) You can lock longer, but it will no longer earn interest beyond that. If you want to re-invest, you can turn around and lock those funds up for another year.